Why viruses hibernate in warm weather

That viruses are seasonal in nature has been known for thousands of years, researchers from Yale and Zurich universities wrote in a paper published this month, as the latest coronavirus was exploding across the United States.

Accounts of respiratory infectious diseases starting in winter date at least to around 400 B.C., in Hippocrates book on epidemics.

The two major contributing factors dictating the spread of viruses are environmental changes and human behavior, the Yale and Zurich study said.

One reason viruses are thought to spread more effectively in winter is that respiratory droplets believed to be a key factor spreading this virus remain airborne for longer in colder weather.

Another potential factor: Viruses degrade more quickly on hotter surfaces, possibly because a protective layer of fat that envelops them dries out quicker, Goodrum said.

The condition of the host organism in the body also is a factor, she said. During the winter, dry forced air, used in many heater devices, can dry out the bodys protective mucosal layers and cilia functions in the nose, Goodrum said. Both the mucosal lining and the cilia small hairs inside the nose remove particulates from the nose before they get into the lungs.

If dry air from a heater compromises those protections, that can increase susceptibility to infection, she said.

Human behavior is also a huge factor.

With colds, for instance, people get them in the summer but not as often, in part because people spend more time outdoors, with winds blowing, doing their own form of social distancing, said professor Kristie Ebi, an epidemiologist at the University of Washington in another coronavirus hot spot, Seattle. You dont get people packed into places where the air circulation is not as good.

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