Public-health experts are less confident in Trump’s prediction. Harvard epidemiologist Marc Lipsitch wrote that the presence of warmer weather, together with the summer closing of schools, is not enough “alone to slow transmission enough to make a big dent.”

“New viruses have a temporary but important advantage — few or no individuals in the population are immune to them. Old viruses, which have been in the population for longer, operate on a thinner margin — most individuals are immune, and they have to make do with transmitting among the few who aren’t. In simple terms, viruses that have been around for a long time can make a living — spread through the population — only when the conditions are the most favorable, in this case in winter.”

“Seasonality does not constrain pandemic viruses the way it does old ones,” Lipsitch writes, citing the 2009 H1N1 flu which started in the spring, receded over the summer, then kicked into high gear in the fall.