Why do covid cases rise in summer, unlike other respiratory viruses?

Traditionally, summer is the season of sunburn and allergies, while winter is a time for sniffles and flu, but now it seems one pathogen is upending our yearly cycle of medical maladies: the coronavirus behind covid-19.

This infection also increases in summer, driving a recent rise in cases and hospitalisations in countries such as the UK, US and France. In England, for example, there were around 180 reported cases per week on average in early April, rising to more than 500 in mid-July.…