The Rules of Asymptomatic COVID Have Changed

In the early days of the pandemic, one of the scariest and most surprising features of SARS-CoV-2 was its stealthiness. Initially, the new coronavirus was only supposed to be transmitted from people who were actively sick – as its predecessor SARS-CoV had done – it turned out to be a silent spreader, also emitting from the airways of people who were unwell. After months of insisting that only symptoms should be masked, tested and isolated, officials scrambled to retool their guidance. Singing, talking, laughing, and even breathing in confined spaces were suddenly classified as threats.

Three years later, the coronavirus is still spreading silently — but the fear of its secrecy seems to be gone. enthusiasm for concealment and testing decreased; Quarantine recommendations have been scaled back, and may soon disappear entirely. “We no longer communicate about asymptomatic transmission,” says Saskia Popescu, an infectious disease epidemiologist and infection prevention expert at George Mason University. “people think, what is the point? I feel good.

Although the concern about asymptomatic spread has dissipated, the threat itself has not. Even as our concerns about the virus continue to shrink and be put aside, the virus — and the way it spreads among us — continues to change. Which means our best ideas for stopping its spread are not only memorable; They are going to become obsolete.

When SARS-CoV-2 was new to the world and almost no one had immunity, it was likely that asymptomatic spread was responsible for Most of the spread of the virus—at least 50 percent or so, says Megan Fitzpatrick, an infectious disease transmission modeler at the University of Maryland School of Medicine. People will not start to feel sick until four, five or six days on average after infection. Meanwhile, the virus may rapidly desiccate itself in the airway, reaching potentially infectious levels a day or two before symptoms begin. Silently infected people weren’t sneezing and coughing — symptoms that push the virus out more forcefully, increasing the efficiency of transmission. But while testing was still scarce and slow to yield results, not knowing they had the virus made them all dangerous. Precautionary testing was still too rare or too slow to produce results. So asymptomatic transmission became the norm, as did epic spread events.

Now, although testing is more plentiful, pre-symptomatic spread is a better known risk, and repeated rounds of vaccination and infection have left layers of immunity behind. This protection, in particular, reduced the severity and duration of acute symptoms, which lowered the risk that people would end up in hospitals or morgues; It might even be in the long COVID chop. At the same time, however, the addition of immunity has made the dynamics of asymptomatic transmission more complex.

On an individual basis, at least, silent diffusion can happen less often than it did before. One possible reason is that symptoms now flare up early in people’s bodies, just three days or so, on average, after infection — a shift that roughly coincided with the appearance of the first Omicron variant and could be a quirk of the virus itself. But Aubree Gordon, an infectious disease epidemiologist at the University of Michigan, told me that faster-arriving diseases may be driven in part by faster immune responses, which are primed by previous exposures. This means that the disease may now coincide with or precede the peak of infection, reducing the average period for which people spread the virus before they feel ill. in that very In a specific sense, COVID could now be a touch more like. Transmission of influenza before symptoms sometimes occur, says Seema Lakdawala, an Emory University virologist. But in general, Gordon told me, “people don’t tend to reach their highest viral levels until after they develop symptoms.”

Combined with more immunity at the population level, this arrangement could work in our favour. People may be less likely to inadvertently pass the virus on to others. Thanks to the defenses we have collectively built up, the same pathogen also has more trouble getting out of infected bodies and infiltrating new ones. That’s almost certainly part of the reason this winter hasn’t been quite as bad as in the past, says Maya Majumder, an infectious disease modeler at Harvard Medical School and Boston Children’s Hospital.

However, many people undoubtedly still catch coronavirus from people who don’t feel sick. Infection Per infection, the risk of juvenile spread may be lower now, but at the same time people are chilling about socializing without masks and testing before gathering in groups—a behavioral change that is bound to negate at least some of the forward shift in symptoms. Pre-symptomatic spread may be less likely at present, but it is not soon gold. Multiply a small amount of prevalence of symptoms by a large number of cases, and that can still lead to…another large number of cases.

There may be some newcomers to the silent group of spreaders, too—those who are now transmitting the virus without showing any symptoms at all. With people’s defenses higher than they were a year and a half ago, infections that might once have been severe are becoming mild or moderate; Those that might have once been mild are now unnoticed, says Syed Mokadams, a computational epidemiologist at the University of York. At the same time, though, immunity may have turned some non-communicable infections into non-transmissible ones, or prevented some people from becoming infected. Absolutely. Milder cases, of course, are welcome, Fitzpatrick told me, but no one knows exactly what these changes add up to: Depending on the rate and degree of each of these mutations, completely asymptomatic transmission may now be more common, less common, or kind of waterlogged.

Better studies of transmission patterns would help cut through the muck; It doesn’t really happen anymore. “To get this data, you have to have very good testing for surveillance purposes, and that basically stopped working,” says Yonatan Grad, an infectious disease epidemiologist at the Harvard School of Public Health.

Meanwhile, people are just doing a live test less, and they rarely report any of the results they get at home. For many months now, even some people who get tested are seeing strings of negative results days into bona fide COVID cases—sometimes a week or more later when their symptoms start. This is concerning for two reasons: First, some legitimate COVID cases are likely to be missed, preventing people from accessing test-based treatments like Paxlovid. Second, inequality confuses the beginning and end of isolation. According to the Centers for Disease Control and Prevention (CDC) guidelines, people who do not test positive until a few days after they become ill should count the first day of onset of symptoms as day 0 of isolation. But if symptoms sometimes outweigh the infection, “I think those positive tests have to restart the isolation clock,” Popescu told me, or risk sending people back into the community too soon.

However, US testing guidelines haven’t undergone a major overhaul in more than a year—right after Omicron exploded across the country, says Jessica Malati Rivera, an infectious epidemiologist at Boston Children’s Hospital. And even if the rules undergo a revamp, they won’t necessarily guarantee more or better testing, which requires access and will. Test programs have been terminated for several months; Free diagnoses are getting rare again.

Through all of this, scientists and non-scientists alike are still grappling with how to define silent infections in the first place. what is considered symptoms It’s not just based on biology, but on behavior — and our vigilance. Jarad told me that as concerns about transmission continue to wane and fade, even mild infections may be mistaken for a quiescent infection. Biologically speaking, the virus and disease may not need to get any fainter to spread easily: forgetting about silent spread may greasing the wheels on its own.


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