This rapid synthesis of knowledge was carried out by Public Health France to help guide the choices of decision-makers and public authorities and their methods of implementation, in accordance with our missions.
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If an attenuation of transmission during the summer in the northern hemisphere is possible, it will probably be modest compared to the effects expected by the control measures put in place.
The transmission of many respiratory viruses evolves periodically, cyclically and seasonally, particularly in the temperate region of the northern hemisphere where increases in incidence are usually observed during fall and winter. The mechanisms associated with this seasonality relate to both the virus and the host. In temperate zones, during autumn and winter, changing weather conditions can contribute to:
- promote the survival of respiratory viruses in the environment and airborne transmission of virions, through lower or moderate levels of temperature, ultraviolet radiation, humidity, precipitation and wind;
- increase host susceptibility, by decreased immunity, brittleness of respiratory mucous membranes, changes in mucus, decompensation or complication of pre-existing health problems;
- modify the behavior of individuals, by promoting indoor social activities and interactions that are more favorable to transmission. [2, 4-7].
This summary describes the results of experimental studies allowing the identification of the environmental conditions modulating the survival of the virus; epidemiological studies ecologically linking the progression of the epidemic and climatic factors in real conditions; and studies projecting the circulation of SARS-CoV-2 under different scenarios of its seasonal behavior and immunity conferred by infection.
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