COVID rates are surging again. Why are you doing so well in the summer?
A mix of human habits and immunity, the environment and SARS-CoV-2 itself explains why the virus appears during the colder months.
By Tanya Lewis
COVID cases have been surging every summer in the U. S. Thanks to summer and meetings.
Scott Olson/Getty Images
It’s that time of year: thick, oppressive heat covers everything, other people gather in air-conditioned homes, offices, retail stores and cafes to rest, and COVID makes a comeback.
Levels of SARS-CoV-2, the virus that causes COVID, have accumulated in wastewater samples across the United States, with the largest increase recorded in the West. The percentage of positive tests is not the best indicator as other people do. getting tested less – has also increased, but hospitalizations have remained relatively low. Most viral respiratory infections, such as the flu, peak in winter. But in the 4 years that SARS-CoV-2 has been circling the world, it has caused spikes not only in winter but also in every summer. The question is, why?
Amanda Montañez; Source: Centers for Disease Control and Prevention
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The imaginable reasons for COVID’s summer spike are complex, but they fall into three main categories: the characteristics of the virus itself, the characteristics of its human hosts, and environmental factors.
SARS-CoV-2 continues to develop new variants. A case appears about every six months, according to Peter Chin-Hong, a professor of medicine at the University of California, San Francisco, who specializes in infectious diseases. In recent weeks, several new subvariants of the Omicron variant of the virus have emerged as dominant, adding variants called “FLiRT” (such as KP. 2 and KP. 3), as well as a more recent variant called LB. These variants could be more transmissible or better able to evade the immune formula than previous ones, says Chin-Hong.
Human behavior and the environment are other most likely points of summer waves. During the summer, many other people gather for events, vacations, or simply spend more time indoors to beat the heat. Winter in the northern hemisphere offers a number of Christmas gatherings. the best for spreading diseases; Similarly, “in the summer, it’s Father’s Day, graduation, the Fourth of July, and then summer travel,” Chin-Hong says. “It’s like a one-two-three shot. “
“We know that almost all [COVID] transmission occurs indoors, in poorly ventilated and/or poorly filtered places,” says Joseph Allen, an associate professor at Harvard University. Chan School of Public Health and director of the Harvard Healthy Buildings Program. “One speculation is that those structural problems and human behavior are causing the accumulation at times in the summer. » Although many offices or other giant buildings have an HVAC formula capable of drawing in cold air from outside, many homes and apartment buildings with window-mounted air conditioners do not. Instead, those air conditioners simply recirculate the stale, virus-laden air in the room.
Some studies have shown that humidity and temperature can also have effects on the transmission of SARS-CoV-2. The virus is most productive when humidity and temperature are low, as cool, dry air holds less moisture, so the microscopic droplets that trap the virus can remain suspended in the air for longer before settling on the ground. But those points are probably less vital than human habit and the characteristics of SARS-CoV-2 itself. At the beginning of the pandemic, scientists thought that summer might simply COVID slows down because the virus is exposed to the sun’s superior heat and more ultraviolet light. “But look at Florida and tropical countries,” Chin-Hong says. “There was no respite. “
Why COVID spreads so well in both summer and winter remains an enduring mystery, while the flu tends to be primarily a winter illness, says Linsey Marr, a professor of civil and environmental engineering at Virginia Tech who specializes in pathogen transmission through aerosols. . ” I’ve been reading the seasonality of influenza for many years and we have some hypotheses as to why it peaks in winter,” Marr says. The first is that the flu virus is more productive in dry situations. Another explanation is that our immune systems are weaker in winter, and a third is that heated buildings are hermetically sealed and recirculate infected air. In the summer, some of those situations occur in cool, air-conditioned buildings, but we don’t see an increase in summer flu. SARS-CoV-2 appears to be more difficult than the flu virus, Marr notes, so there could be situations where the flu can’t.
As climate changes cause more common and severe heat waves across much of the U. S. , the U. S. In the U. S. and the world, other people are likely spending even more time indoors over the summer, just like SARS-CoV-2. This year’s summer wave seems to have begun. on the West Coast, which has already experienced several weeks of intense heat.
And then there’s the human immune system. People’s immunity to COVID may have waned since they were last vaccinated or infected in the fall or winter, making them more likely to get sick. Fortunately, immunity to overexposure, in the form of memory T cells, prevents most people from becoming seriously ill. But the decline in antibodies means that other people may still be inflamed.
Earlier this year, the U. S. Centers for Disease Control and Prevention issued a report on the U. S. Centers for Disease Control and Prevention. U. S. citizens encouraged others over the age of 65 to get a second booster dose of last fall’s COVID vaccine. But less than a quarter of adults have gotten even a first booster dose since last fall. recommends that if you haven’t been vaccinated in the last year, you deserve to do it now. Older adults, especially those who are immunocompromised, planning a trip, or attending a giant collection like a wedding, also deserve a moment. reinforcement. And the Food and Drug Administration recently legalized a new edition of the vaccine for the fall, targeting the FLiRT KP. 2 variant or its predecessor, JN. 1.
Of course, there are other steps other people can take in the face of COVID in the summer, and many of them will be familiar: wearing a mask, breathing cleaner indoor air by expanding ventilation and filtration, and cleaning crowded indoor spaces.
Today, four years after the emergence of COVID, most people have some level of immunity to SARS-CoV-2 through vaccination, infection, or either. And the virus is no longer as deadly as it once was (although it still poses a danger to other people with chronic illnesses or who are immunocompromised, and long COVID remains a risk). At this point, Allen says, it’s better to find more structural solutions, such as redesigning buildings to allow for healthy, open air and temperature, rather than having to choose between the two. it’s about energy power or empty indoor air,” says Allen. “I reject that. And everyone deserves to reject that. We can have either of the two things.
Tanya Lewis is a medical and fitness editor at Scientific American. She writes and edits articles for the print magazine on topics ranging from COVID to organ transplants. She is also the co-host of Scientific American’s Your Health, Quickly en Science, the Quickly podcast, and writes the weekly health newsletter
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