People's perception and cost effectiveness of home confinement during an influenza pandemic: evidence from the

Keywords: people's behavior, cost-benefit analysis, home confinement, epidemics, prevention measures, public health interventions JEL Classification: I12, I15, I18, H51, C15

People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case

Caroline Orset Orset

Introduction

New influenza epidemics have emerged in the past century. Spanish Flu (1918-1920), Asian Flu (1957-1958), Hong Kong Flu (1968-1969), Russian Flu (1977-1978), H 1 N 1 Flu Pandemic (2009-2010), avian influenza A (H 7 N 9 ) virus ( 2013) are examples. [START_REF] Achonu | The financial impact of controlling a respiratory virus outbreak in a teaching hospital: lessons learned from SARS[END_REF] These epidemics have a high speed of propagation that generates many victims. The 2009 H 1 N 1 epidemic highlighted the importance of the use of home confinement 2 on a large scale to fight against emerging diseases. In March 2009, an influenza pandemic H 1 N 1 emerged in Mexico. Since 1 st August 2010, more than 214 countries have been affected by this epidemic, which has claimed over 18,449 deaths. [START_REF] Ashenfelter | Using Mandated Speed Limits to Measure the Value of a Statistical Life[END_REF] As the vaccine has not yet been produced, only non-pharmaceutical interventions have been recommended by the World Health Organization (WHO) (Perez Velasco et al, 2012). One of them is home confinement. Many countries have applied it on a voluntary basis, while others like China have imposed it (Liang et al, 2012).

Home confinement is not a common preventive measure in the face of an influenza pandemic in France. Thus, what attitude the French would adopt if this measure were put in place? Would this measure be economically cost-effective? Based on Haber et al (2007), we define home confinement as the recommendation that infected persons and members of their household stay at home for seven days. [START_REF] Blendon | Attitudes toward the use of quarantine in a public health emergency in four countries[END_REF] Our approach is based on two building blocks. First, we contribute to the literature in epidemiology by studying perceptions and individual behavior in the face of a home confinement policy to prevent the influenza epidemics. Understanding people's behavior is necessary to define health policy. Indeed, as discussed in Zhu et al (2017), individual behavior within society determines the impact of the epidemic. An individual who does not want to comply with preventive measures would become more and more dangerous to themselves and the rest of society. Therefore, it is necessary to determine in advance individual reactions when deciding on public health policy. The literature lacks data on how individuals will behave in the face of a home confinement policy during an influenza epidemic. This article is the first to fill this gap. We use a stated preference method. Kroes and Sheldon (1988) and Louviere et al (2000) present and develop the use of this method in diverse fields. We then conduct a questionnaire to elicit the preferences of individuals. In the questionnaire, we place respondents in a hypothetical context in which an epidemic has been reported. We put them in different situations: first, [START_REF] Achonu | The financial impact of controlling a respiratory virus outbreak in a teaching hospital: lessons learned from SARS[END_REF] For more details see: http://www.who.int/influenza/en/ and http://www.cdc.gov/flu/index.html. [START_REF] Adda | Economic Activity and the Spread of Viral Diseases: Evidence from High Frequency Data[END_REF] For the World Health Organization (WHO), the home confinement policy is to separate the infected (isolation) and all members of their household, even if they are in good health (quarantine), from other individuals, asking them to stay at home. [START_REF] Ashenfelter | Using Mandated Speed Limits to Measure the Value of a Statistical Life[END_REF] For more details, See: http: // www. Who.int/csr/don/2010 08 06/en/index.html. they have been in contact with at least one infected person; second, they have been in contact with at least one infected person and medical assistance is provided during home confinement; third, they have not been in contact with infected persons. For each situation, we ask them to choose the maximum number of days they will be willing to stay at home. In fact, asking for the number of days, as opposed to asking directly whether the respondent would comply with home confinement is a way to evaluate the duration that the respondents would voluntarily be willing to stay at home by removing the efficiency aspect of the sanitary measure. Thus, it avoids a deviation of behavior if this measure was to be applied in case of epidemics. From respondents' answers, we elicit the proportion of respondents who are willing to comply with home confinement, which is people who have answered a number of days equal or higher to seven days. We find that more than three quarters of respondents would comply with home confinement.

Deciding to be willing to comply with home confinement during an influenza epidemic depends on an individual's characteristics (age, income, composition of the household and professional group), the interaction one can have with an infected person (meeting or not), and the conditions of home confinement (medical assistance or not) but not on having real experience of preventive measures. We discuss the different behaviors that emerge from this study, such as sensitivity to certainty, egoism and altruism.

Second, our paper is linked to the literature dealing with cost-benefit analysis of infectious disease prevention measures. Many studies have been conducted on the impact of a disease using a cost-benefit study. For example, Achonu et al (2005) use a costbenefit analysis to study the financial impact of combating a respiratory virus epidemic in a teaching hospital. Gupta et al (2005) and Mubayi et al (2010) focus on an emerging infectious disease, SARS, and compare the costs of different quarantine strategies. However, Adda (2016) is the only study that estimated the cost of influenza in France, but its evaluation only concerned the impact on influenza spread of school and public transport closure policies. Focusing on the economic impact of the home confinement policy on influenza is therefore new in economic literature. We try to recognize, identify, evaluate, measure and value the costs of influenza and home confinement in France. We use detailed data on the prevalence, the incidence of the disease and the incidence rate from the French GPs Sentinelles network. [START_REF]Interim pre-pandemic planning guidance: community strategy for pandemic influenza mitigation in the United States[END_REF] These data have the particularity of proposing age groups (children, adults and the elderly), which is very useful given that influenza does not affect people in the same way according to age. However, building a mathematical model on the reduction of the influenza incidence with a home confinement policy in force is difficult largely because of the small amount of occurrences in France and therefore the shortage of data. Because of the difficulties in calculating realistic estimates of the reduc- tion of influenza incidence due to home confinement, we focus on the incidence reduction threshold from which home confinement is cost-effective. We find that the measure of home confinement would be a prevention track not to be dismissed. By comparing our results with the existing literature (Longini et al., 2005, and Haber et al., 2007, which have done stochastic simulation models of influenza epidemics in other countries) and the stated method approach, we see that this measure would be cost-effective.

The article is organized as follows. Section 2 presents the study and details the characteristics of the disease and of home confinement policies. Section 3 shows the results on the perception and behavior of the French in the face of home confinement during an epidemic. Section 4 proposes to study the cost-effectiveness of the measure.

Section 5 concludes.

The study

In this section, we give an overview of the characteristics of the influenza as well as details on home confinement. We then present the survey we analyze.

Influenza characteristics and home confinement

We consider one of the major viral diseases: influenza. The principal symptoms of influenza are fever, chills, cough, headaches, diarrhea, sore throat, runny nose, body aches and fatigue. The affected individuals become contagious one day before the onset of the first symptoms and remain so for five days. Symptoms appear one to three days after contamination. The influenza usually lasts one week. [START_REF] Chao | a publicly available stochastic influenza epidemic simulation model[END_REF] In France, influenza affects between 1 and 4 million people each year, and causes between 1,500 and 2,000 deaths, mainly among people over 65. [START_REF] Cobanoglu | A comparison of mail, fax, and Web-based survey methods[END_REF] Influenza viruses are easily transmitted from person to person by air. In the event of a reported epidemic, personal protective measures, such as wearing a mask, are recommended in order to avoid being infected or infecting the others. For influenza, vaccines exist but the immunity is not acquired following vaccination. Moreover, the constant genetic changes in influenza viruses require that the composition of the vaccine be adjusted every year. Indeed, the vaccine for influenza has a low efficacy due to the variability of influenza strains. WHO decides in February on the composition of the vaccine to be used in the October vaccination campaign. Then, the vaccine is manufactured according to the circulating strains, but some strains can mutate. This is what happened in France Preventive measures must be taken by public health authorities to prevent (before the vaccine is found) or to supplement the use of the vaccine (when the vaccine exists).

Influenza spreads rapidly, especially when there are high concentrations of populations (public transportation, communities). According to the WHO, reduction of contact intensity by home confinement (isolation and quarantine) and social distancing is highly effective in reducing the incidence of influenza, especially in the early stages of the pandemic (Chao et al, 2010; Halder et al, 2010; Kelso et al, 2009; Milne et al, 2008).

We then focus our analysis on home confinement as a health prevention measure in the case of influenza. This measure consists of recommending to persons infected and their

Target respondents

To analyze the perception of the French population for home confinement, we use a stated method approach. This method allows us to analyze the choices stated by individuals in order to express individual behavior in relation to a given situation. A questionnaire has been drawn up in which, as an introduction to the respondent, we explain that home confinement consists of staying at home with contact only with the members of one's household and that the characteristics of pandemic flu (symptoms, duration...). We then place the respondent in a hypothetical situation in which an epidemic has been reported and they have been in contact with an infected person (CH Contact). We then ask them to choose the maximum number of days they will be willing to confine themselves to home, i.e., staying at home without outside contact. We ask them the same question by adding the intervention of medical assistance, which is the visit of a health care professional who verifies the state of health of the respondent during home confinement (CH HWV). This 1 suggest that the two groups are not significantly different. [START_REF] Couper | Web surveys: A review of issues and approaches[END_REF] For more details on Marketest, see: http://www.marketest.co.uk/. [START_REF] Fricker | An experimental comparison of Web and telephone surveys[END_REF] Influenza can affect everyone, so selecting a sample based on the characteristics of the French population does not present a risk of selection bias. [START_REF] Gupta | The economic impact of quarantine: SARS in Toronto as a case study[END_REF] We do not have the perception of children in this study. In France, interviewing a child requires many administrative procedures. We did not hire them because a child will listen to the decision of their parents, that is, the choice of an adult. As a result, children's behavior is associated with adult behavior. Based on the control questions, we find that few people practice a medical profession (about 6%). Our panel therefore does not present an over-representation of the medical sector that could be a selection bias.12 63% of respondents support a criminal sanction for non-respect of mandatory preventive measures during an epidemic period. Blendon et al (2006) show that in the United States a compulsory home confinement policy is only supported by 42% of the population. Finally, 14% of respondents have already experienced preventive measures such as mask wearing, home confinement etc. for an influenza pandemic, cough or meningitis. The hypothetical bias is reduced for these respondents.

Results

We now analyze the answers of respondents. If the number of days chosen is lower than seven days, the respondent is deemed not willing to comply with the home confinement

Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y policy. On the other hand, if it is equal to or higher than seven days, the respondent is willing to do so. We then study the determinants of the respondent's decision to comply or not with home confinement.

Descriptive analysis

Figure 1 presents the proportion of people who are willing to comply with home confinement, which is people who have answered a number of days equal or higher to seven days. Each situation, that is to say having been in contact with an infected person (CH Contact), having been in contact with an infected person and having the visit of a health professional during home confinement (CH HWV), and not having been in contact with an infected person (CH No contact), is shown. confinement when they have not been in contact with a contaminated person. The elderly verify the certainty effect of Kahneman and Tversky (1979). They prefer to eliminate risk rather than reduce it. The elderly are sensitive to certainty. Finally, selfish behavior by respondents is highlighted. Altruistic behavior would mean that an individual who is more likely to become contaminated and thereby contaminate others, decides to confine themselves to their home to avoid contact with others. In our study, being in contact with an infected person makes respondents (adults and elderly) less likely to confine than not to be in contact. Thus, if the individual risk of being contaminated and therefore of contaminating others is higher, the proportion of respondents in agreement with confinement is lower. This indicates selfish behavior on the part of the respondents.

Determinants of choice

We now investigate the impacts of the respondents' characteristics (gender, age, number of people living in the household, monthly net income, professional group, and experience (whether the respondent has already experienced prevention measures against epidemics)

on the respondent's choice to comply with home confinement. We use a Probit model. [START_REF] Ferguson | Strategies for containing an emerging influenza pandemic in Southeast Asia[END_REF] An individual i has some propensity to confine to home, y * i , linearly related to a vector of observable variables, x i , and others factors we cannot observe, the error term, i :

y * i = αx i + i .
When y * i is greater than zero, the individual i is willing to comply with home confinement. We cannot observe the individual i's propensity to comply with home confinement, only the actual choice, which we will call y i and yields a value of one when the individual i is willing to comply with home confinement and zero when he is not. The probability that y i = 1 is given by:

P (y i = 1|x i ) = Φ(x i β)
where Φ is the cumulative density function for the standard normal. Hence, we note y i the individual i's choice to comply with home confinement (No=0, Yes=1), the quantitative variable Age, x 1 i , and the qualitative variables, which are Gender (Male=0, Female=1), x 2 i , People living in the household (1 person=1, 2 persons=2, 3 persons and more=3), We first observe that for all proposed situations, the older a respondent is, the more likely they are to be willing to comply with home confinement. Moreover, the lower the respondent's income, the more likely they are to be willing to comply with the recommendations (e -0.122 = 0.885 < 1, e -0.134 = 0.875 < 1, and e -0.152 = 0.859 < 1, respectively).

x 3 i ,
In addition, in the situation in which the respondent has been in contact with an infected person, the larger the number of family members, the more likely they are to be willing to comply with home confinement (e 0.171 = 0.186 > 1). Finally, in the situation where the respondent has been in contact with an infected person and a health professional visits them during confinement, the higher the index (from 1 to 5) of their professional group, the more likely they are to be willing to comply with home confinement (e 0,127 = 1, 135 > 1). Blendon et al (2006) observe that in regions where people have greater experience of emergency measures, such as Singapore, Taiwan and Hong Kong, the population is less willing to comply with preventive measures like wearing a mask, temperature measurement and quarantine. We then analyze more precisely the link between the choice to comply with home confinement and the individual's experience. In our panel, only 28 over 200 respondents have already experienced preventive measures. From Table 3, we find that there is no link between the decision to comply with home confinement and the individual's experience (all the p-values of the Chi2 test are greater than 0.05). In addition, we note that the rates of people with experience who state that they are willing to comply with home confinement and those who state that they are not are identical for all the situations. By analyzing the data, we see that some individuals do not have the same decisions depending on the situations proposed, but that the changes in the decision compensate each other. Thus, people's behavior changes with culture. In France, having real experience of preventive measures is not a decision-making factor for choosing or not choosing to comply with home confinement. Therefore, it is not necessary to make public health expenditures for simulation exercises addressed to the population. [START_REF] Kahneman | Prospect Theory: An Analysis of Decision under Risk[END_REF] Respondents may change their behavior according to situations. We then analyze the impacts of the respondents' characteristics (gender, age, people living in the household, Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y monthly net income, socio-professional categories) on the change in decisions in favor of being willing to comply with home confinement between two situations. The independent variables are defined as in Table 2. We use a Probit model again by taking y * i the propensity to change one's decision in favor of being willing to comply with home confinement. If respondents were not willing to comply with home confinement when they have been in contact with an infected person, the younger they are, the more they will change their minds if a health care professional visits them during home confinement or when the interaction with an infected person did not take place. In addition, if respondents were not willing to comply with home confinement when they were in contact with an infected person, the lower the number of family members, the more likely they are to change their minds when the interaction with an infected person did not take place (e -0.247 = 0.781 < 1).

Cost-benefit analysis of home confinement

We propose to make a cost-benefit analysis. No study has been made on the economic efficiency of home confinement policies for reducing the incidence of influenza in France. We first estimate the cost of influenza in France by age class (Children, < 18 years old; Adults, 18 -64 years old; Elderly, > 64 years old). Adda (2016) has proposed a cost evaluation of influenza in France. We then take this evaluation as a basis and update it with data that are more recent. We obtain Table 5. We note that according to age, different costs are considered and their value differs.

For children, the cost is divided between a medical cost (otitis media, pneumonia, hospitalization), the loss of human capital, the loss of parent productivity and the death of children cost. The medical cost is the lowest cost because the probability that influenza

Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y degenerates into otitis media and pneumonia is low. However, the loss of human capital represents a high cost. [START_REF] Kelso | Simulation suggests that rapid activation of social distancing can arrest epidemic development due to a novel strain of influenza[END_REF] We take the same assumptions than Adda (2016) but we update the results with more recent data. We assume that sick children miss school for 3 days implying a reduction of about 0.8 percent of their human capital in that year. We assume a return to schooling of 5 percent per year. The net present value of earnings over the life cycle (42 years) is calculated with an annual discount factor equal to 0.95. We consider individuals to live 15 years in retirement. This yields a loss of 92.88 euros per influenza episode. As a child cannot supervise himself, an adult (most often the mother) has to be at home during their illness. This creates a loss of productivity based on the median female income, weighted by the labor market participation of women. This induces a large cost of 95.70 euros. We then use the value of a statistical life (VSL) which quantifies the benefit for the society of avoiding a fatality. For adults, we consider that on average an adult infected by influenza does not go to work during two days. This implies a loss of productivity due to their absence from work of ca. 74 euros, and an additional loss of productivity when they work at 50 percent of their capacity, around 12.96 euros. For evaluating the cost of death, we adopt the same method than for the children. We get a low risk of death around 4.82 per 100,000. Then, we add medical costs for GP visit and hospitalization. These costs represent a small expenditure compared to the overall cost. [START_REF] Kroes | Stated Preference Methods: An Introduction[END_REF] Finally, the costs for the elderly are divided between the medical cost and the cost of death. Medical cost is much higher than for children and adults, at 695 euros. Moreover, the probability of death is large, 205.19 per 100,000, implying a large cost of death. [START_REF] Liang | Response to the first wave of pandemic (H 1 N 1 ) 2009: experiences and lessons learnt from China[END_REF] Then, we estimate the cost of home confinement in France. Research on the cost-benefit analysis of prevention measures for infectious diseases has considered different types of cost measures including costs to society, costs to individuals (Coudeville, 2009), qualityof-life measures (Newall et al, 2007), etc. In general, costs can be divided into direct and indirect costs. Direct costs are all expenditures for continuing care, health care providers, certain household expenditures (meal and delivery, home energy), hospitalization, per- [START_REF] Kelso | Simulation suggests that rapid activation of social distancing can arrest epidemic development due to a novel strain of influenza[END_REF] As Smith (1776) states: The acquisition of ... talents during ... education, study, or apprenticeship, costs a real expense, which is capital in [a] person. Those talents [are] part of his fortune [and] likewise that of society. [START_REF] Kreuter | Social desirability bias in CATI, IVR, and Web surveys: The effects of mode and question sensitivity[END_REF] In Adda (2016), the loss of human capital was 99 euros, the loss of productivity was 102 euros, the probability of death was 0.7 per 100,000, and the VSL was between 1.6 and 6 million euros. [START_REF] Kroes | Stated Preference Methods: An Introduction[END_REF] In Adda (2016), absent from work was 78.90 euros, reduced productivity was 13.80 euros, the probability of death was 4 per 100,000, and the VSL was between 1.6 and 6 million euros. [START_REF] Liang | Response to the first wave of pandemic (H 1 N 1 ) 2009: experiences and lessons learnt from China[END_REF] In Adda (2016), the probability of death was 102 per 100,000, and the VSL was between 1.6 and 6 million euros.

Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y sonal wage employed for the sanitary measures. Indirect cost is the productivity loss cost due to the absence of the individual to its work, the productivity loss cost due to the closure or the lack of frequentation of public place and the cost of death. We try to recognize, identify, list, measure and value these costs in Table 6. Table 6 displays the costs of home confinement. We have considered the same age group as for the costs of influenza. We take as a reference the age of the infected person.

As home confinement concerns all household members including the infected person, we have evaluated the costs for the entire household according to INSEE (2013-2014). In order to calculate the costs of a representative household, we have used the weight that each household composition represents in France from INSEE (2013-2014).

For each age group, we assume the possibility of setting up medical surveillance, i.e., a health care professional coming every day to take health news from the confined. Being confined at home implies that meals must be delivered for each family member as well as an additional cost of energy (power, gas, water ...). Finally, we also factor in the loss of production of shops, museums, movie theaters... due to the absence of consumers.

When a child is infected, a parent must stay at home to watch them. A household of one person cannot include children age group. We assume that a three-person household consists of two adults and one infected child; a four-person household of two adults and two children (including an infected child); a five-person household of two adults and three children (including an infected child); and a six-person household of two adults and four children (including an infected child). We added to the medical costs and the cost of death, the adult costs of absenteeism (absence and loss of productivity) and loss of human capital for each confined child.

When an adult is infected, all costs related to their illness and absence from work have been identified (absence from work and loss of productivity). We assume that a one-person household includes an infected adult; a two-person one 26.6%, one child and one infected adult, or 73.4%, two adults (including one infected adult); Finally, when an elderly person is infected, we assume that a household of one person includes: an infected elderly person; a two-person one includes two elderly people (including one infected elderly person); a three-person one, three elderly people (including one infected elderly person); a four?persons household four elderly people (including one infected elderly person), a five-person one five elderly people (including one infected elderly person); and finally a six?person household will consist of six elderly people (including one infected elderly person). In France, few elderly people live in a household consisting of more than two people. When that is the case, this means that they share their dwelling with other elderly people (for example in a retirement home). Today, few seniors live with their children.

We now turn to the cost-benefit analysis. For evaluating the incidence and the prevalence of influenza in France, we use the French GPs Sentinelles network, which compiles of large databases on disease prevalence, incidence and incidence rate in France. This network is made up of 1,300 general practitioners (2.2% of all practitioners in France)

and about a hundred voluntary, liberal pediatricians. The member physicians are called "Sentinel physicians". [START_REF] Louviere | Stated Choice Methods, Analysis and Applications[END_REF] In 2017, the network continuously collected information on eight health indicators (seven infectious diseases and one non-infectious indicator). [START_REF] Lusk | Effects of cheap talk on consumer willingness to pay for golden rice[END_REF] The Institut de Veille Sanitaire (lnVS) implemented this network as a public health surveillance system in 1984.

Figure 2 displays the time series patterns of incidence rates at the national level and on a weekly basis between 2005 and 2014. [START_REF] Mcdonald | A comparison of online and postal data collection methods in marketing research[END_REF] Each year, we observe recurrent peaks of influenza during the winter season. However, the amplitude of these peaks varies little.

It does not appear to diminish or increase over time.

Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y

2005_01 2005_14 2005_27 2005_40 2006_01 2006_14 2006_27 2006_40 2007_01 2007_14 2007_27 2007_40 2008_01 2008_14 2008_27 2008_40 2009_01 2009_14 2009_27 2009_40 2009_53 2010_13 2010_26 2010_39 2010_52 2011_13 2011_26 2011_39 2011_52 2012_13 2012_26 2012_39 2012_52 2013_13 2013_26 2013_39 2013_52 2014_13 2014_26 2014_39 2014_52
Infection rate per 100,000 Week Figure 3 displays the average incidence rates within a year, by calendar month, from January to December. As seen in the previous graph, influenza shows strong seasonal patterns with a peak in winter (in February) and a low incidence between mid-spring and mid-fall (from May to August).

Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y This means that in 2013-2014 only 38.3% of adults and children were vaccinated while 51.9% of the elderly were vaccinated. Conf , the rate reduction in the incidence due to confinement at home for the aggregated population (without any distinction of age class), Cost All Conf , average of the costs with home confinement per case for the children, the adults and the elderly in euro, Cost All Inf lu , average of the costs of influenza per case for the children, the adults and the elderly in euro. [START_REF] Milne | A small community model for the transmission of infectious diseases: comparison of school closure as an intervention in individual-based models of an influenza pandemic[END_REF] Table 7 presents the set of the parameters used to calculate the cost effectiveness of the confinement measure. We consider the average prevalence and the average incidence from the data of the French GPs Sentinelles network from 2005 to 2014, the costs with home confinement per case from table 6 and the costs of influenza per case from Table 5. For the costs of home confinement, we make a distinction between the presence (With HWV) or not (Without HWV) of a medical assistance during home confinement. The costs are higher with medical assistance. We first note that the higher the benefit for the society of avoiding a fatality and/or the lower the proportion of individuals complying with home confinement, the lower the rate reduction threshold. Therefore, based on cost-benefit analysis, to implement home confinement, health decision-makers will be more inclined to be less demanding about the level of reduction in the impact of this measure when the benefit to society of avoiding death is high. On the other hand, the more the measure will be respected by more individuals, the more the level of reduction required will be high. We then observe that the increased costs of the measure linked to the medical assistance during home confinement must be offset by an increase of the rate of incidence reduction for the measure to be cost-effective. Finally, we note that the rate reduction threshold of incidence is higher when we differentiate age class than when we consider the aggregated population. Thus, by not differentiating by age classes, the public decision-maker may consider that the measure is cost-effective whereas it is not when differentiation is taken into account. This shows the interest of considering age classes in a study on influenza epidemics.

Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y

As we mentioned, in France, there are no epidemiological studies on the reduction of the incidence rate due to home confinement. Nevertheless, some have been made in other countries. Longini et al (2005) show that for 70% of people who follow home confinement in Southeast Asia, [START_REF] Mubayi | A cost-based comparison of quarantine strategies for new emerging diseases[END_REF] the rate reduction in the incidence due to confinement at home is at 99.91% for a basic reproduction number R 0 = 1.4, at 99.7% for R 0 = 1.7, at 98.5%

for R 0 = 2.1, at 85% for R 0 = 2.4. [START_REF] Murphy | The Value of Health and Longevity[END_REF] Moreover, Haber et al (2007) evaluate that for 70% (80%) of people who follow home confinement in a small urban US community, the rate reduction in the incidence due to confinement at home is at 83% (91%) for R 0 = 2.7. We can note that the results of these studies are convergent, although the countries considered do not have the same size and the same density of population and although their environmental characteristics differ. Would a home confinement policy be cost-effective if we consider that the reduction of the incidence rate of these studies would apply for the influenza epidemic in France?

We then compare the lines for which the proportion of individuals complying with home confinement is at 70% and 80% in Table 8 and the rate reduction of incidence data from these studies. We observe that whatever the way of calculating the rate reduction threshold of incidence and whatever the pandemic severity level, home confinement would be cost-effective.

From our stated method approach, we have understood the proportion of people who would comply with home confinement (see Figure 1). Children were not questioned in our study. We used the parents' answers for them (Adult category). Three situations were proposed. In order to implement home confinement, we consider that the infected person has been in contact with an infected person (CH Contact); has been in contact with an infected person and will seek medical assistance during their home confinement (CH HWV); or has not been in contact with an infected person. In addition, we assume that if the infected person is willing to comply with home confinement, all household members will be confined with them. We propose to analyze the cost-effectiveness of home confinement from the stated answers of our survey. Table 9 presents the results. [START_REF] Mubayi | A cost-based comparison of quarantine strategies for new emerging diseases[END_REF] That is, 70% of those infected and their household members agreed to stay confined to home while 30% refused. [START_REF] Murphy | The Value of Health and Longevity[END_REF] The basic reproduction number (R 0 ) is one of the commonly accepted measures of pandemic severity. R 0 is defined as the average number of secondary infections, produced by a typical infected case in a very susceptible population. From Ferguson et al. (2005), Mills et al. (2004), and Uribe-Sanchez et al (2011), R 0 values for influenza range between 1.4 and 3.9, where R 0 ≤ 1.8 are considered as of low transmissibility and 2.2 ≤ R 0 ≤ 3.9 as of high transmissibility. These studies have been done in Southeast Asia, for reproducing the 1918 pandemic influenza around the world, and in Florida (United States), respectively.

As previously, it is worth highlighting the interest of differentiating by age class instead of taking the aggregated population. The rate reduction threshold of incidence varies between 65.88% and 84.13% with differentiated age classes, and between 49.24% and 65.05% with the aggregated population. According to the existing studies carried out in other countries, we observe that a 10% increase in the proportion of people who comply with home confinement strongly increases the incidence reduction rate. For instance, from Haber et al (2007), when 70% of people comply with the measure, the reduction rate is 83% while it is 91% with 80% of people complying. In our stated approach, we find that the level of home confinement stated by respondents is between 75.90% and 94.44%. Hence, taking into account the existing studies, we can estimate that in France, home confinement would be cost effective regardless of the pandemic severity level and the VSL value.

Conclusion

This paper aims to support home confinement as a preventive measure in the context of influenza epidemics. We first probe perceptions and attitudes towards complying with home confinement in France. We conclude that knowing the level of voluntary participation for this type of measure is essential. This measure cannot be implemented if the population decides not to participate. It would seem inconceivable to assign a police officer to each person detected as infected to verify that they comply with confinement.

In addition, assessing people's participation also makes it possible to estimate whether the measure will be economically effective from a public health perspective.

We find that over three quarters of respondents indicate compliance with home confinement. Deciding to be willing to comply with home confinement during an influenza epidemic depends on an individual's characteristics (age, income, household composition and professional group), the interaction with an infected person (meeting or not), and the conditions of home confinement (medical assistance or not). However, having real experience of preventive measures does not factor significantly in the decision to comply or not. Moreover, we highlight selfish behavior by respondents. When they are more likely to become contaminated and thereby contaminate others, they are less willing to comply with home confinement. However, this behavior may also be explained by a certainty bias that pushes people to believe that they are taking all necessary measures to avoid contamination. Finally, we also observe that respondents may behave altruistically when dealing with their own family. Indeed, not staying home during an epidemic limits the risk of contamination of next of kin, especially in large families.

When considering preventive measures, the health decision-maker needs to analyze whether the measure is cost-effective. We find that taking into account age may sharpen the analysis. According to the VSL value and the proportion of people who comply with confinement, we assess the level of the incidence reduction rate threshold for which the measure is cost-effective. No epidemiological study has examined or estimated the reduction in influenza incidence following the implementation of home confinement in France. However, estimates from studies in other countries converge to very close values.

From our stated method approach and from the existing studies, this allows us to estimate that in France, the home confinement policy would be cost-effective regardless of the pandemic severity. However, the epidemiological model would be useful for determining the exact impact of home confinement in France. We expect that our study will trigger additional research in this direction. Moreover, as influenza epidemics know no borders, it would also be interesting for this work to be extended to other countries. Indeed, our study can easily be replicated in other regions or countries.

Our paper has certain limitations. First, as in all preference approaches, there may be hypothetical biases and controversies or incorrect messages leading to confusion or misunderstanding by participants in our study. As suggested by Lusk (2003), we tried to reduce the hypothetical bias by using "cheap talk" 30 to explain the home confinement policy and the characteristics of pandemic flu (symptoms, duration...) before asking the [START_REF] Newall | Costeffectiveness analyses of human papillomavirus vaccination[END_REF] Cheap talk refers to process of explaining hypothetical bias to individuals prior to asking a valuation question.

Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y first question to respondents. Second, the data collection method could be discussed. We used an online study. Online studies save time and effort in collecting data (Cobanoglu et al., 2001, Couper, 2000 and McDonald and Adam, 2003) and provide better quality responses with fewer "Do not know" answers (Fricker et al., 2005, Kreuter et al., 2008, and Heerwegh and Loosveld, 2008). Therefore, as far as the quality of the collected data is concerned, online studies do not seem to present more disadvantages than other types of surveys.

  during the winter 2014-2015, when the flu caused over 18,000 deaths among people who Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y had been vaccinated against the flu.

Figure 1 :

 1 Figure 1: Proportion of people (in percentage) who comply with home confinement according to the different situations. Adults (166 respondents), Elderly (36 respondents), All (200 respondents).

  Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y

  [START_REF] Longini | People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case[END_REF] a three-person one: two adults (including one infected adult) and one child; a four-person one: two adults (including one infected adult) and two children; a five-person one two adults (including one infected adult) and three children; and a six-person one two adults (including one infected adult) and four children. Home confinement for other family members results in costs: for children, there is a loss of human capital due to their absence from school, and for adults the costs attributable to their absence from work. 21 From INSEE 2013-2014. Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y

Figure 2 :

 2 Figure 2: Weekly incidence rates of influenza, 2005-2014.

Figure 3 :Figure 4

 34 Figure 3: Incidence rates of influenza over calendar year. Average 2005-2014.

  Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y

Table 1 :

 1 Socio-economic characteristics of respondents. 200 respondents.

	Comment citer ce document :
	ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home
	confinement during an influenza pandemic evidence from the French case. European Journal of
	Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y

Table 2 :

 2 Determinants of choice to comply with home confinement.

	Model: Probit model
	Endogenous variable	CH Contact CH HWV CH No contact
	Gender	-0.077	0.100	0.059
		(0.201)	(0.217)	(0.221)
	Age	0.015*** 0.022***	0.017**
		(0.005)	(0.005)	(0.007)
	People living in the household	0.171**	0.052	0.026
		(0.079)	(0.082)	(0.086)
	Monthly net income of the household	-0.122**	-0.134**	-0.152**
		(0.056)	(0.058)	(0.061)
	Professional group	0.061	0.127*	0.068
		(0.067)	(0.071)	(0.095)
	Experience	0.568	0.406	0.405
		(0.357)	(0.369)	(0.368)
	Observations	200	200	200
	McFadden's R²	0.054	0.078	0.083
	Log-likelihood	-100.932	-84.093	-83.637
	*p<0.1; **p<0.05; ***p<0.01. Standard errors are in parenthesis.

Table 3

 3

shows the Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y

contingency tables

[START_REF] Halder | Analysis of the effectiveness of interventions used during the 2009 A/H 1 N 1 influenza pandemic[END_REF]

and the test on independence (Chi-2 test).

[START_REF] Heerwegh | Face-to-face versus Web surveying in a high-Internet coverage population: differences in response quality[END_REF]

Table 3 :

 3 Link between experience and choice to comply with home confinement.

	CH Contact
	No experience Experience Total
	No home confinement	24.4	10.7	22.5
	Home confinement	75.6	89.3	77.5
	Total	172	28
	Chi-2 test=2.593 (p-value=0.107)
	CH HWV
	No experience Experience Total
	No home confinement	20.9	10.7	19.5
	Home confinement	79.1	89.3	80.5
	Total	172	28
	Chi-2 test=1.600 (p-value=0.206)
	CH No contact
	No experience Experience Total
	No home confinement	18.0	10.7	17.0
	Home confinement	82.0	89.3	83.0
	Total	172	28
	Chi-2 test=0.912 (p-value=0.339)

Table 4

 4 sums up the results.

Table 4 :

 4 Determinants of choosing to change decision in favor of being willing to comply with home confinement between two situations.

	Model: Probit model
	Endogenous variable	HC Contact/HC HWV HC Contact/HC No contact
	Gender	-0.458	0.052
		(0.338)	(0.224)
	Age	-0.032***	-0.009*
		(0.008)	(0.005)
	People living in the household	-0.126	-0.247***
		(0.116)	(0.091)
	Monthly net income of the household	0.077	-0.010
		(0.082)	(0.061)
	Professional group	-0.101	-0.032
		(0.104)	(0.005)
	Observations	200	200
	McFadden's R²	0.021	0.025
	Log-likelihood	-32.896	-77.145
	*p<0.1; **p<0.05; ***p<0.01. Standard errors are in parenthesis.

Table 5 :

 5 Costs of influenza per case, in euro. Data on costs and healthcare use are taken from Prosser et al. (2006) for children, from Nichol (2001) for adults and from Molinari et al. (2007) for the elderly. These studies weight medical costs by the probability of health care usage. Data on mortality from influenza by age group comes from the National Vital Statistics Reports, Vol 65, No 4, June 2016. We have taken the average rate of mortality from 2005 to 2014 by age group. Data on wages are taken from INSEE, "Revenus salariaux médians des salariés de 25 à 55 ans selon le sexe en 2014" (http://www.insee.fr/fr/themes/tableau.asp?reg id=0&ref id=NATnon04146). Labor market participation data comes from OECD skill data set. All US dollars converted into euros with an exchange rate of 0.8. Loss of human capital is costed using a return to schooling of 5 percent, median wages by sex and average labor market participation by sex over a period of 42 years. Net present value numbers are displayed, calculated with a discount factor equal to 0.95.

	Children
	GP visit (32% chance)	6.68
	Otitis media (0.28% chance)	17.38
	Pneumonia (12% chance)	16.45
	Hospitalisation (0.07% chance)	2.45
	Hospitalisation (sequelae pneumonia 0.7 per 100,000)	3.61
	Loss of human capital (3 days off school, 5% return)	92.88
	Parent stays home (50% of time, labor market particip. 0.65)	95.70
	Value of statistical life	1.3-7.5 million
	Probability of death	1.71 per 100,000
	Cost of death	22-128
	Adults
	Absent from work (2 days of work at average wage)	74
	Reduced productivity (0.7 days at 50%)	12.96
	GP visit (45% chance)	9.45
	Hospitalisation (0.04% chance)	1.80
	Value of statistical life	1.3-7.5 million
	Probability of death	4.82 per 100,000
	Cost of death	63-361
	Elderly
	Outpatient visit	219
	Hospital	476
	Value of statistical life	1.3-7.5 million
	Probability of death	205.19 per 100,000
	Cost of death	2667-15389
	Notes.

Table 6 :

 6 Costs associated with home confinement per case, in euro.converted into euros with an exchange rate of 0.8. Loss of human capital is costed using a return to schooling of 5 percent, median wages by sex and average labor market participation by sex over a period of 42 years. Net present value numbers are displayed, calculated with a discount factor equal to 0.95. Cost of meals (meal and delivery) is given from http://www.dependance-infos.com/maintien-a-

	1 person	2 persons	3 persons	4 persons	5 persons	6 persons

National Vital Statistics Reports, Vol 65, No 4, June 2016. We have taken the average rate of mortality from 2005 to 2014 by age group. Data on wages are taken from INSEE, "Revenus salariaux médians des salariés de 25 à 55 ans selon le sexe en 2014" (http://www.insee.fr/fr/themes/tableau.asp?reg id=0&ref id=NATnon04146). Labor market participation data comes from OECD skill data set. All US dollars Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y

  25 Figure 4: Yearly incidence of influenza, by age, 2005-2014. For i ∈ {Children, Adults, Elderly}, we define the average annual costs of home confinement in euros, C Conf , and the average annual costs of influenza in euros, C Inf lu , , the average of declared cases (infected persons) for the age class i, p i Conf , the proportion (in percentage) of cases i complying with home confinement, n i Inf lu , the average incidence for age class i, 1 -r Conf , the rate reduction in the incidence due to home confinement, Cost i Conf , costs with home confinement per case for the age class i in euro, Cost i Inf lu , costs of influenza per case for the age class i in euro. We also define the average annual costs of home confinement for all aggregated age groups in euro, C All Conf , and the average annual costs of influenza for all aggregated age groups in euro, C All Inf lu , as, Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y

	0 1000000 2000000 3000000 4000000 5000000 6000000 7000000 as, respectively: 2005 Incidence (number of cases) C Conf = 2006 Children 2007 i (n i d + n i Adults 2008 Inf lu * r Conf )(p i 2009 Year Elderly 2010 Conf * Cost i 2011 All age groups 2012 Conf + Cost i 2013 Inf lu ) and C Inf lu = i (n i d + n i Inf lu ) * Cost i Inf lu , with n i C All Conf = (n All d + n All Inf lu * r All Conf )(p All Conf * Cost All Conf + Cost All Inf lu ) and C All Inf lu = (n All d + n All Inf lu ) * Cost All Inf lu , with n All d , the average of declared cases (infected persons) without any distinction of age 2014 class, p All Conf , proportion (in percentage) of cases (without any distinction of age class) complying with home confinement, n All Inf lu , the average incidence without any distinction d respectively: of age class, 1 -r All
	25 Data	from	CNAM-TS,	http://invs.santepubliquefrance.fr/Dossiers-
	thematiques/Maladiesinfectieuses/Maladies-a-prevention-vaccinale/Couverture-
	vaccinale/Donnees/Grippe.

Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y

Table 8 :

 8 Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y (With HWV). Table 8 presents the results according to the VSL value and the proportion (in percentage) of individuals complying with home confinement. Rates reduction threshold of incidence, 1 -r Conf and 1 -r All Conf .

		Threshold for	Threshold for	Threshold for	Threshold for
		VSL= 1.3 million €	VSL= 4 million €	VSL= 5 million €	VSL= 7.5 million €
	Proportion of cases
	complying with home
	confinement	1-r Conf 1-r All --	Conf	1-r Conf 1-r All --	Conf	1-r Conf 1-r All --	Conf	1-r Conf 1-r All --	Conf
				Without HWV
	10%	36.89% 17.36% 25.45% 12.53% 23.47% 11.98% 19.94% 11.10%
	20%	53.94% 29.60% 40.60% 22.27% 38.04% 21.40% 33.27% 19.99%
	30%	63.76% 38.69% 50.65% 30.06% 47.96% 29,00% 42.80% 27.27%
	40%	70.15% 45.71% 57.81% 36.44% 55.16% 35.27% 49.96% 33.34%
	50%	74.64% 51.29% 63.16% 41.76% 60.62% 40.53% 55.54% 38.48%
	60%	77.97% 55.84% 67.32% 46.26% 64.90% 45,00% 60,00% 42.88%
	70%	80.53% 59.62% 70.63% 50.12% 68.34% 48.84% 63.66% 46.70%
	80%	82.57% 62.80% 73.35% 53.46% 71.18% 52.19% 66.70% 50.04%
	90%	84.22% 65.52% 75.61% 56.39% 73.55% 55.13% 69.28% 52.99%
	100%	85.59% 67.88% 77.51% 58.97% 75.57% 57.73% 71.49% 55.62%
				With HWV
	10%	39.65% 18.71% 27.40% 13.12% 25.23% 12.48% 21.34% 11.46%
	20%	56.83% 31.54% 43.05% 23.20% 40.32% 22.20% 35.19% 20.56%
	30%	66.43% 40.88% 53.16% 31.20% 50.36% 29.98% 44.91% 27.98%
	40%	72.56% 47.99% 60.24% 37.69% 57.52% 36.35% 52.10% 34.13%
	50%	76.81% 53.58% 65.47% 43.06% 62.89% 41.66% 57.64% 39.32%
	60%	79.93% 58.09% 69.50% 47.59% 67.06% 46.16% 62.04% 43.75%
	70%	82.32% 61.80% 72.69% 51.45% 70.39% 50.02% 65.62% 47.58%
	80%	84.21% 64.92% 75.28% 54.79% 73.12% 53.36% 68.58% 50.93%
	90%	85.74% 67.57% 77.42% 57.70% 75.39% 56.29% 71.08% 53.88%
	100%	87.00% 69.85% 79.23% 60.26% 77.31% 58.87% 73.22% 56.49%

  34. Smith, A. Recherches sur la nature et les causes de la richesse des nations. 1776. 35. Uribe-Sánchez, A., Savachkin, A., Santana, A., Prieto-Santa, D., Das, T.K. A predictive decision-aid methodology for dynamic mitigation of influenza pandemics. OR Spectrum. 2011;33(3):751-786. 36. Viscusi, W.K., Aldy, J.E. The Value of a Statistical Life: A Critical Review of Market Estimates throughout the World. Journal of Risk and Uncertainty. 2003; 27:5-76. 37. Zhu, G., Chen, G., Fu, X. Effects of active links on epidemic transmission over social networks. Physica A. 2017;468:614-621.

Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y

The French GPs Sentinelles network is a national system of clinical surveillance that collects real-time epidemiological data from general practitioners and pediatricians in France.

For more details see: http://www.who.int/influenza/en/.

From the French GPs Sentinelles network and Institute Pasteur in France.

For more details see: http://ec.europa.eu/food/animals/animal-diseases/controlmeasures/avianinfluenza/index en.html.

According to the INSEE in 2013, the health sector staff represents 6.5% of the working population.

Our choice is based on the Probit model because choosing a Logit model would imply a higher probability attributed to extreme events, compared to the choice of a normal distribution.

A contingency table is a type of table in a matrix format that displays the (multivariate) frequency distribution of the variables. It provides a basic picture of the interrelation between two variables and can help find interactions between them.

The chi-2 test is used to determine whether there is a significant difference between the expected frequencies and the observed frequencies in one or more categories.

We are not talking here about the importance of simulating an epidemic in a hospital or other medical centers.

For more details see: https://websenti.u707.jussieu.fr/sentiweb/?page=presentation.

Acute diarrhea, Chickenpox, Herpes zoster, Influenza, Lyme disease, Male urethritis, Mumps and Suicidal attempts.

Actually, data from 1985 exists but we could not access to the age classes.

Although there is a time lag between the occurrence of different patients, the costs are calculated over a period of one year. We then consider that the discount rate is equal to one.

We discussed with the French GPs Sentinelles network to verify whether data were available or whether an epidemiological model had been produced concerning the impacts of home confinement on the incidence of influenza in France. Unfortunately, there is none.

Comment citer ce document : ORSET, C. (Auteur de correspondance) (2018). People's perception and cost effectiveness of home confinement during an influenza pandemic evidence from the French case. European Journal of Health Economics, 1-16. , DOI : 10.1007/s10198-018-0978-y We consider that home confinement is cost-effective when the average annual costs of home confinement, C Conf , are lower than or equal to the average annual costs of influenza, C Inf lu , and for the aggregated population, i = All, when the average annual costs of home confinement for all aggregated age groups, C All Conf , are lower than or equal to the average annual costs of influenza for all aggregated age groups, C All Inf lu . Building a mathematical model on the reduction of the influenza incidence with home confinement prevention in France is difficult largely because of the very few occurred cases in France and therefore the shortage of data. [START_REF] Molinari | The annual impact of seasonal influenza in the US: Measuring disease burden and costs[END_REF] In fact, only two cases occurred when at the end of December 2016, residents (66 people) of a retirement home in Moselle (Northeast France) and a retirement home (80 people) in Saint-Gengoux-le-National (Center-East France) were confined to reduce the spread of influenza. Because of the difficulties in calculating realistic estimates of the rate reduction in the incidence due to home confinement, we propose to evaluate the rate reduction threshold in the incidence due to home confinement for which the home confinement policy is cost effective. We then calculate this threshold, 1 -r Conf when all the age class are differentiated, and 1 -r All Conf for all aggregated population, such that C Conf = C Inf lu and C i Conf = C i Inf lu , respectively. We consider two options for home confinement: without medical assistance (Without HWV) and with medical assistance