In this study, we investigated the level and distribution of vaccination acceptance against the 2009 H1N1 influenza virus during the peak of the epidemic in France. This provided an exceptional opportunity to investigate the impact of social and health conditions on vaccination behavior in the context of spreading of an emerging infectious disease. To the best of our knowledge, few studies have examined the role of these factors in the epidemiology of pandemic A (H1N1) influenza immunization in the general population. On the basis of this telephone survey performed in December 2009, the rate of vaccination acceptance, which includes self-reported intentions or actions of immunization, could be estimated at about one quarter (27.4%) of the French population ≥ 16 years of age. More precisely, actual vaccination against the pandemic H1N1 influenza virus was estimated at 7.5%, which is congruent with the more or less 10% estimate of the vaccination rate calculated by the French Ministry of Health from the number of persons who received the vaccine in the vaccination centers for the immunization period 2009-10 
. Concerning the socio-demographic distribution of vaccination acceptance among French adults, our data have shown that the male, older and more advantaged participants – who are characterized by higher educational and material resources – were more likely to accept the vaccine. Surprisingly, with the notable exception of sex, these results are quite comparable to those of many epidemiological surveys conducted in developed countries about seasonal influenza vaccination 
. Indeed, a large range of socioeconomic variables such as age, education level and income have consistently been demonstrated to influence influenza vaccination behaviors. Nevertheless, after controlling for other potential confounding variables, we found that vaccination acceptance was much more determined by individuals’ experiences of seasonal influenza vaccination in previous years than by age, which is consistent with the available data from various surveys related to pandemic influenza 
Noticeably, vaccination acceptance was not considerably higher among the participants belonging to the categories that were identified as priority groups for pandemic vaccination by the public health authorities. As indicated in table 1, only the respondents affected by chronic diseases or pregnancy were found to report a significantly higher rate of vaccination acceptance. To further examine the influence on these factors on vaccination acceptance, a simultaneous logistic regression was performed to control for other potentially confounding socio-demographic variables. Interestingly, health condition dropped out as a predictor, suggesting that risk factors are perhaps only indirectly associated with attitude toward vaccination through the influence of a range of socio-demographic variables such as age or occupational status. On the contrary, professional status was found to significantly affect vaccination acceptance after adjusting for other socio-demographic variables. This might be attributable to the fact that those working in the health or childcare fields were subjected to more immediate and personal pressures from their social and institutional environment. Nevertheless, the effects of social conformity remained relatively weak since less than one third of members of this key target group were likely to accept vaccination. Overall, the rate of acceptance of pandemic influenza vaccination among health and childcare workers was not substantially different from those observed for seasonal influenza in previous years in European countries 
At this stage, it remains necessary to uncover the reasons why certain persons or groups were more likely to accept immunization against the 2009 pandemic H1N1 influenza virus than others, even when socio-demographic variables, as well as risk factors, were controlled for. In the recent literature, one of the dominant strategies has been to use open-ended questions within large-scale surveys. This type of questioning is known to encourage more complete and meaningful answers in surveys by permitting subjects to express their motivations and/or sentiments in their own phrasing 
. In the present study, the primary reasons associated with acceptance and rejection of vaccination can be broadly divided into 3 groups. The first group addresses the mental representation of the threat – in particular the beliefs and judgments related to the severity of the illness and risk factors (i.e., which groups are more vulnerable to the infection), as well as the emotional response to the risk of contracting the disease. The second relates to the perception of the vaccine, including concerns about its safety or effectiveness. The third group of motives can be associated with issues of trust toward those advocating the vaccine (the government, the pharmaceutical industry, or biomedical experts) – including beliefs in conspiracy theories.
Eventually, the motivations that underlie the acceptability of vaccination could be approached to a large extent from a traditional risk/benefit analysis. According to this basic model of decision-making under uncertainty, the acceptance or rejection of any protective action should be interpreted as the outcome of a trade-off between the risks and personal or societal benefits associated with products or activities that are recognized for their preventive value. From this theoretical perspective, the public acceptability of vaccination is expected to vary roughly as a direct function of both perceived risk and perceived benefit. Moreover, the perceived benefit associated with immunization depends in turn, for a large part, on the perceived risk of contracting the disease – which is generally known to result from two main cognitive components: the personal likelihood of becoming infected (vulnerability) and the seriousness of the consequences of that infection (severity). Although the relevance of the risk/benefit approach would deserve a more complex discussion that is beyond the scope of this article, most of the primary reasons that were spontaneously invoked by the respondents might indicate that people actually perform a sort of trade-off between the perceived risk and the perceived benefit associated with the vaccine uptake.
For example, among the principal reasons for the non-acceptance of vaccination were (1) belief that the vaccine against the 2009 pandemic H1N1 influenza virus is dangerous or ineffective and (2) belief that the pandemic influenza is not a serious illness, suggesting that the perceived risk exceeds the perceived benefit associated with pandemic influenza vaccination. Thus, almost half of the reluctant respondents (47.0%) indicated that they had doubts about either safety or efficacy of the pandemic vaccine, and more than one quarter (27.9%) felt that the pandemic H1N1 influenza could be considered to be a minor illness. Finally the motives captured by open-ended questions provided results that are largely consistent with those of previous quantitative and qualitative studies on the determinants of seasonal influenza vaccine acceptance. According to certain reviews of literature, the fear of side effects can be easily identified as one of the most commonly reported barriers to vaccination across all communicable diseases 
Several limitations can be pointed out in this study. First, even if the sampled population did not significantly differ from the general population in terms of age, gender, occupation and place of residence, it cannot be ruled out that the subjects who refused to participate in our study were characterized by a range of psychological and/or sociological attributes that made them different from the cooperating subjects with regards to vaccination acceptance or non-acceptance. Second, the timing of the survey (early December) might have led to both an underestimate of the vaccination coverage rate, and an overestimate of vaccination intention among the French adult population since the controversy about the safety and/or necessity of the pandemic H1N1 influenza vaccination was growing over time. As noted above, the actual vaccination coverage rate was assessed at the end of the domestic outbreak by the Ministry of health and found to include approximately 10% of the French. Third, the nature of reasons offered by the participants to justify their acceptance or refusal to get vaccinated against the pandemic influenza might have been subject to possible biases of social desirability (or conformity). This typical bias – which describes the subjects’ propensity to report a range of reasons for a particular behaviour that are different from their “real” motivation because they are viewed as more socially acceptable – has been extensively well-documented in the methodological literature 
To conclude, the results of this study tend to show that the 2009 pandemic H1N1 influenza was not perceived by the French population to be significantly different from the seasonal influenza. Notably, the distribution and justification of vaccination acceptance among the participants were strongly similar to those of seasonal influenza vaccination acceptance 
, and consequently contributed to the maintenance of health inequalities in France. In this regard, it should be noted that the pandemic H1N1 influenza has been commonly and ironically named “grippette” (little flu) in France. Thus, as long as the patterns of mortality and/or morbidity associated with the pandemic influenza did not differ crucially from those related to the recent seasonal influenza, it would probably have been difficult to observe substantially higher vaccination coverage rates for this emerging infectious disease among the various key subgroups within the French population. In terms of risk communication, these results have one major implication: the failure of the immunization campaign cannot be solely attributed to the controversy about the potential side effects of the vaccine, but also to the nature and level of the perceived risk associated with the pandemic H1N1 influenza. From this point of view, a public health information campaign that primarily focuses on convincing people of the safety of the vaccine would likely be less fruitful than expected.