Seasonality of COVID-19, Other Coronaviruses, and Influenza

Will the incidence of COVID-19 decrease in the summer?

There is reason to hope that it will, since in temperate climates influenza and the four coronaviruses that are among the causes of the “common cold” do follow a seasonal pattern, with many fewer cases in the summer. If COVID-19 is affected by season, this would obviously be of importance for policies regarding “lockdown” and provision of health care resources. Furthermore, understanding the reasons for seasonal variation might point towards ways of controlling the spread of COVID-19 (caused by a coronavirus sometimes referred to as SARS-CoV-2, though I’ll usually ignore this pedantic distinction).

I’ll look here at the evidence for seasonality in influenza and the common cold coronaviruses, and to what extent one might expect COVID-19 to also be seasonal. I’ll consider three classes of possible reasons for seasonality — seasonal changes in virus survival and transmissibility, in human resistance to infection, and in social behaviour. I’ll then consider whether we might be able to enhance such seasonal effects, further reducing the spread of COVID-19 in summer, and also extend these effects to winter.