(CN) – At this point, Covid-19 season has spanned the entirety of 2020. But research published in Frontiers in Public Health on Monday postulates whether the SARS-CoV-2 virus will continue to emerge with winter weather — just like cold and flu — once humans reach herd immunity.
“The virus is here to stay,” said Dr. Hassan Zaraket, an assistant professor at the American University of Beirut and an author on the paper.
To date, the disease has killed 925,000 people worldwide and is the third leading cause of death in the U.S. In nine months, the virus spread throughout six continents, infecting 29 million people to date, including 24,310 people in Lebanon, where Zaraket lives.
On average, 267,000 people tested positive for Covid-19 daily over the last week.
While Zaraket anticipates continued outbreaks and a rise in infections this winter, he said Covid-19 may adapt to patterns of seasonal transmission once communities reach herd immunity and overall transmission drops.
“Some people might confuse that when herd immunity is reached then [Covid-19] will be extinguished,” Zaraket said. “This is not the case. We still need time to achieve herd immunity and it’s obvious that until then the virus will continue to circulate irrespective of seasons.”
Cold, dry weather is commonly associated with an increase in respiratory tract infections like bronchitis, the common cold and the flu. Part of it is biology, with lower temperatures weakening the human immune system and strengthening the lipid viral envelope protecting the pathogens.
Part of it is also sociology, as cold weather drives people indoors — increasing opportunities for disease transmission.
Since SARS-Cov-2 was first detected in Wuhan, China, at the very end of 2019, researchers have yet to study the disease through fall and winter.
“Virus transmission has been more aggressive in the temperate regions where winter is prevailing. This indicates that cold and dry conditions might promote SARS-CoV-2 infections,” the researchers wrote in their report.
While studies in China predicted disease transmission would reduce in warmer weather, other studies have since emphasized that temperature changes alone do not prevent the virus from spreading.
“The highest global Covid-19 infection rate per capita was recorded in the Gulf states, regardless of the hot summer season,” said collaborating author Dr. Hadi Yassine, of Qatar University in Doha, in a statement. “Although this is majorly attributed to the rapid virus spread in closed communities, it affirms the need for rigorous control measures to limit virus spread, until herd immunity is achieved.”
Short of the development of a vaccine — and its availability — the world’s best protection against Covid-19 has been to avoid catching it entirely. But that has also led to quarantines and lockdowns worldwide with devastating economic side effects.
“I think that the major component is human behavior that is different in warm weather versus cold weather,” said Dr. Thomas Jaenisch, an epidemiologist at the University of Colorado's Anschutz Medical Campus who was not affiliated with the study. “If it's cold, people are going to be inside more and maybe closer together, and this is going to affect transmission more than the physics of the transmission for droplets under different climate scenarios [like] temperature, UV light, humidity.”
As research continues to develop, public health experts continue to promote wearing a mask, maintaining social distance and handwashing.
“In addition, we should develop a sense of what are situations that could lead to a cluster of cases,” Jaenisch added. “Have a diary of how many of these situations did I have in the last week or the last two weeks so that if I'm diagnosed at some point, I can really help the health authorities by saying, OK, in the last two weeks, there's these two situations that I've been in a cluster.”
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