At face value, it seems highly plausible that SARS-CoV-2—the virus that causes COVID-19—could behave seasonally, being more prevalent in winter and less so in summer. The four other coronaviruses that commonly circulate in humans behave in this way. We’ve also seen COVID-19 cases, hospitalisations and deaths spike over winter in the UK and other countries, which is suggestive of a seasonal effect.