It is a conclusion we find almost impossible to accept now — not just popularly, but as academic students too. Historians are biographers of an age, and like any biographer, we like to think our period was an agent of change. “Millions dead: things go on as before” makes for a poor quotation on the flyleaf of a new book.

The latest biological findings on SARS-Cov-2 viral entry into human tissue and cough-droplet ballistics suggest that the major transmission mechanism are not fine aerosols but large droplets, and thus, warrant the wearing of surgical masks by everyone.

In recent days, the media has been full of stories about such COVID-19 super-spreaders, including in Italy, South Korea, Britain, and Boston. These stories sometimes are presented as tragic one-off case studies. Yet their statistical impact is enormous. As of March 12th, for instance, roughly 80 percent of Massachusetts’ COVID-19 cases could be traced to a single corporate meeting. In Italy, genetic analyses suggest that the country’s epidemic originated with just two people.