In case you haven’t noticed, the days are getting shorter and, in most parts of the United States, also cooler. Winter will soon descend upon the northern hemisphere along with several vacation-prone and family-centered holidays that may tempt many people to celebrate in ways they have wisely resisted for most of the Covid-19 pandemic.
At the same time, the coronavirus responsible for the pandemic is surging worldwide and throughout this country, where new cases have risen to over 150,000 a day. Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said last June that exactly this could happen unless aggressive action was taken to thwart the virus’s spread.
Last month, following widespread failure to take such action, Dr. Fauci predicted that if we don’t now do what we know is needed this fall and winter, we could be facing as many as 400,000 Covid-related deaths by year’s end.
And our annual infectious visitor, the influenza virus, promises to complicate the picture, causing its own surge of debilitating infections that each year claim the lives of tens of thousands of Americans.
For more reasons than most people realize, both flu and coronaviruses have the ability to spread more easily from person to person during the colder, drier days of winter. The risk is not limited to the fact that in colder weather people spend more time indoors potentially exposed to others who may harbor and spread an infectious virus. The risk is also influenced by lower temperatures and relative humidity that can increase the viral load of the air we breathe.
Of course, far more is understood about the behavior of the influenza virus than the novel coronavirus that is now causing such havoc. Rossi A. Hassad, an epidemiologist and statistician at Mercy College in Dobbs Ferry, N.Y., reported this month that both viruses “share key transmission characteristics.” Dr. Hassad and other experts say that what is known about the flu virus can inform our understanding of how and why Covid-19 is likely to become even more hazardous in the months ahead and that this knowledge can, in turn, reinforce the advice that everyone adopt readily available measures to thwart it.
Alas, we cannot afford to wait for a safe and effective Covid-19 vaccine. Despite the intense excitement last week over an early report from Pfizer of a very promising experimental vaccine in the research pipeline, it may be six months or longer before this or any vaccine is likely to be widely available to protect most Americans against the potentially devastating infection.
“The fatality rate associated with Covid-19 is at least 10 times higher than from the flu,” Dr. Hassad said in an interview. “And the Covid virus is more efficiently transmitted by both respiratory droplets and aerosols, which are smaller than respiratory droplets.”
In colder, drier air, he explained, respiratory droplets lose water content and become smaller and lighter and thus able to linger in the air for longer periods, creating “a perfect recipe for exposure to a higher viral load” both indoors and out.
“Low humidity during the winter enables the influenza virus to live longer indoors, and this together with spending more time indoors and in closer contact, significantly increases the risk of transmission and infection,” Dr. Hassad wrote in MedPage Today.
Furthermore, both the influenza virus and the SARS-CoV-2 virus that causes Covid-19 have a fatty outer membrane that keeps them structurally sound and protects the RNA they contain that infects cells, causing disease. In temperatures at or near freezing, this fatty membrane solidifies into a gel, forming a rubbery coat that helps the virus survive and move more readily from person to person in cooler weather.
Characteristics of our own nasal passages in the colder, drier months enhance the risk of infection by these viruses. Nasal passages become dry and more susceptible to damage when the humidity is low, making it easier for viruses to invade the body.
These factors, along with “a high level of transmissibility (including asymptomatic transmission) and virulence of SARS-CoV-2, create a perfect recipe for an even more explosive pandemic” in the coming months, Dr. Hassad noted. Given the fact that the vast majority of people have no immunity to Covid-19, he wrote, it “has the potential to parallel the 1918 flu pandemic if we fail to comply with the protective measures recommended by public health authorities.”
Dr. Stanley M. Perlman, a microbiologist at the University of Iowa who has studied coronaviruses for more than four decades, said in an interview that the “key variables” for a new explosion of Covid infections “are people spending time indoors in not well-ventilated places and not wearing masks.” While air exchange in a hospital unit takes place 12 times an hour, indoor air in a typical room in a private home is exchanged only once or twice an hour, on average.
Dr. Perlman emphasized, “This is a remarkably contagious virus. Things have gotten worse and will get worser still. Our biggest worry is Covid-19 fatigue. People are losing respect for the virus and letting their guard down, which is a bad idea.” Even outdoors, he said, “if you’re standing one foot away from someone and not wearing a mask,” you could transmit or contract the virus.
“The nose and mouth are the virus’s portal of entry,” Dr. Hassad said. “How can a mask not be a barrier against an organism coming toward me? There’s been an obvious difference in infections where masks are being worn consistently. It’s common sense, and it’s not a huge burden.”
Or as Michael Osterholm, epidemiologist and infectious disease expert at the University of Minnesota and a member of President-elect Joseph R. Biden Jr.’s task force on Covid, put it, “Sharing air with someone is the primary mode of transmission.” He suggested two protective approaches: physically (though not socially) distancing yourself from others whose viral health you have no way of knowing, or creating a “bubble” of people who remain highly faithful to safe practices.
“The integrity of that bubble is only as good as its weakest link,” he said. “If one person lacks fidelity, everyone else is at risk.” He suggests meeting with friends and relations in outdoor settings, wearing masks and maintaining physical distance.
Instead of indoor gatherings of family and friends in the upcoming holidays, Dr. Osterholm said that “the ultimate gift you can give people you love is not to get anybody infected. This is your Covid year — just get through it — then hope that next year we’ll be in a very different situation. We’re going to see the darkest days of this pandemic between now and next spring,” when a vaccine may become available.