Numerous epidemiological studies have shown that individual and collective behaviors play a fundamental role in the spread of infectious diseases. This is why it is important, from a perspective of prevention and health promotion, to understand how populations react to infectious risks, and why some people adopt highly protective behaviors while others do little, whether in terms of hygiene or social interaction.

However, until the COVID-19 pandemic, there was little research on the determinants of behavioral responses to respiratory infectious diseases. This is likely due to the fact that the last major epidemics to strike Europe or North America occurred in the 1950s and 1960s. Yet the social sciences only began to take a serious interest in health-related behaviors starting in the 1980s…

Consequently, in our work we had to rely on explanatory models designed to understand population responses to the risks of degenerative diseases, such as cancer or cardiovascular disease. In particular, we selected variables that could potentially explain health-promoting behaviors drawn from three highly compelling approaches in the field of non-infectious diseases:

• the sociocultural approach, which has repeatedly demonstrated the existence of a social gradient in attitudes toward illness (particularly based on the economic and cultural capital available to individuals);

• the psychosocial approach, which takes into account interindividual variables such as social support or trust;

• and finally, the social-cognitive approach, which emphasizes normative and factual beliefs to explain differences in individuals’ responses to illness.

Our first surprise was the very high level of compliance among the French public with public health measures to combat the pandemic. During the first weeks of the pandemic, nearly 95% of our fellow citizens reported following the main preventive measures recommended by public authorities. These figures may seem quite surprising when viewed through the lens of cultural stereotypes that portray the French as a rather uncivil and undisciplined population!

Even though we cannot completely rule out some distortion of behavioral reality on the part of our respondents, these results have been confirmed by international studies, particularly through the analysis of mobility data collected via cell phones, where self-reporting biases do not exist…

Regarding explanatory factors, we found that only a small number of them played a key role in the adoption of protective behaviors. To begin with, we observed that sociocultural and psychosocial factors that are usually strongly correlated with behaviors—such as education or occupational status—played a relatively minor role in the adoption of preventive measures.

Thus, only the age and, to a lesser extent, the gender of respondents appear to have had a lasting impact on adherence to health recommendations. In fact, the variable that best explained preventive behaviors was the social norm perceived by the subjects: it is as if, in this complex epidemiological situation, our fellow citizens had spontaneously aligned themselves with what they perceived as the expected behavior within their circle of friends or family.

Of course, since there are notable psychological differences between emerging infectious diseases and degenerative diseases—the former generally being less well-known and less predictable than the latter—we should not have expected the factors explaining behavior to be exactly the same in both cases.

To begin with, it is important to remember that it is difficult to significantly improve a situation in which the level of compliance and cooperation among the population—and particularly among the groups most at risk—is already very high. This is what economists call diminishing marginal returns: convincing the last few “holdouts” to adopt preventive measures is extremely costly, and in some cases even counterproductive.

However, in the long term, as people’s behavior begins to relax due to weariness with measures that are undeniably restrictive, it may be helpful to remind them of the social norm—that is, the behavior of the majority.

Similarly, it may be useful to make it known that adopting protective behaviors is not only valued or supported by public authorities or healthcare professionals, but also by the vast majority of our fellow citizens. This type of strategy relies on our predisposition toward conformity, which applies equally to health-promoting behaviors and risky behaviors.

In the fields of disease prevention and environmental health, there is now ample experimental evidence showing that reminding people through various communication channels of the dominant social norm within a group or community helps to sustain a process of change…