COVID-19 AND THE SEASONS—PRELIMINARY SCIENTIFIC THOUGHTS
SCIENCE—NOT “FEELINGS” or hunches—should guide our response to the COVID-19 pandemic. On March 20, 2020, Science, the weekly journal of the American Association for the Advancement of Science, published “Sick Time,” a discussion of COVID-19 and seasonality by Jon Cohen. He writes, “Dozens of diseases wax and wane with the seasons. Will COVID-19?”
It’s a nontrivial question, with multiple aspects arising in preliminary scientific assessments. Here are tidbits gleaned from Cohen’s Science article
together with my usual Internet sleuthing. For impatient sorts, science tells us it’s too early to tell.
Some Epidemics Are Seasonal. Research by Micaela Martine of Columbia University has suggested that at least 68 infectious diseases are seasonal.
A Calendar of Epidemics. Old data appear here because introduction of vaccines largely mitigated these diseases. Image from Science, March 20, 2020.
Polio, for example, was predominately a summer affliction; influenza was and continues to be a late winter phenomenon. On the other hand, Cohen notes, “… many have no seasonal cycle at all. So no one knows whether SARS-CoV-2, the virus that causes COVID-19, will change its behavior come spring.”
What’s more, he writes, “Even for the well-known seasonal diseases, it’s not clear why they wax and wane during the calendar year.” Polio epidemics of the Fifties, for example, led to closing of swimming pools, which had virtually nothing to do with spread of the virus.
Epidemiologist Scott Dowell heads vaccine development and surveillance at the Bill & Melinda Gates Foundation. In the Science article, he observes that “All kinds of things are seasonal, like Christmas shopping.” He cautions that it’s easy to be misled by spurious correlations.
Yet, Dowell notes, “If we knew what suppressed influenza to summer-time levels, that would be a lot more effective than any flu vaccines we have.”
Seasonality Has Many Influences. Some diseases are spread by insects that thrive during rainy seasons. Others are affected by either relative humidity (the value reported in weather reports: how close the air is to saturation), absolute humidity (the total amount of water vapor in a given volume of air), or abrupt changes of humidity.
Is COVID-19 a winter disease? Then what about its occurrence in warm, humid Singapore or antipodal Australia? Or does it thrive in cold weather because people tend to congregate in enclosed environments?
Maybe It’s Us Being Seasonal. Cohen writes, “There’s evidence of seasonal variation in the actions of human immune genes as well.”
“In a massive analysis of blood and tissue samples from more than 10,000 people in Europe, the United States, Gambia, and Australia, researchers at the University of Cambridge found some 4000 genes related to immune function that had ‘seasonal expression profiles.’ ”
Columbia University’s Macaela Martinez has identified diurnal cycles of human immune systems. She has also initiated a study of how artificial lighting affects this.
A Conclusion from Science. Cohen writes about Martinez’s work: “The global COVID-19 emergency may bring more attention to the research and help speed discoveries, she says. But for now, no one knows whether rising humidity, longer days, or some as-yet-unsuspected seasonal effect will come to the rescue—or whether humanity must confront the pandemic without any help from the seasons. Time will tell.” ds