About those new isolation guidelines…

How do we live with COVID-19?

This is a question MIT has been asking and answering repeatedly for the last two years. The Institute’s response to this question has evolved with time, viral variants, and the advent of effective vaccines. And it will continue to change, says Medical Director Cecilia Stuopis. “This virus is not going away,” she emphasizes. “It will continue to adapt, and so will we.”

The new CDC guidelines, which have been adopted by the Massachusetts Department of Public Health and MIT, represent the latest answer to the question of how we live with the virus. Even as cases surge, driven by the more transmissible Omicron variant, the updated guidelines reduce the isolation period for infected individuals from 10 full days to five after a positive test result — or after symptom onset, if symptoms come later — as long as the individual is asymptomatic at that point or symptoms are mild and improving. Those five days of isolation must be followed by five days of strict masking around others.

It’s a change that has been met with skepticism in some quarters. “The reasoning behind the shift to a shorter isolation period could have been better communicated at the time,” Stuopis acknowledges, “But while economic considerations and concern about disruption to critical services may have been factors, I also believe that these guidelines represent a growing realization that the virus is here to stay. And I think they are a valid response to the circumstances and the current science.”

The CDC points to hundreds of studies showing that the amount of virus in the noses of infected individuals generally peaks around the time of symptom onset and declines rapidly thereafter. Although infectious virus has been cultured from nasal samples up to nine days following symptom onset, researchers have repeatedly failed to document viral transmission occurring later than about a week after symptoms begin. One study that examined transmission patterns between 730 infected individuals and their 8,852 close contacts in mainland China showed that infected individuals were most likely to transmit the virus to others from about two days prior to symptom onset through the two to three days that followed. A more rigorous contact-tracing study in Taiwan found no transmission occurring later than six days after symptom onset — this despite the fact that the 2,761 close contacts in this study included nearly 700 healthcare workers who were not wearing appropriate personal protective equipment at the time of exposure.

There’s also more recent evidence that vaccinated people who become infected may clear the virus faster than people who are not vaccinated. A Singaporean study of 218 vaccinated and unvaccinated individuals infected with the Delta variant showed that, while both groups had similar viral loads at time of diagnosis, Ct levels (a measure of the amount of virus present in the nose) decreased faster in vaccinated patients — about three days faster, on average. Another study analyzed nearly 20,000 viral samples obtained from 173 infected individuals — 36 vaccinated, 137 unvaccinated — who were part of the National Basketball Association’s occupational health program between late November 2020 and mid-August 2021. As in the Singaporean study, researchers reported similar peak viral levels in both groups, but vaccinated subjects cleared the virus in an average of 5.5 days, compared with 7.5 days for unvaccinated individuals. “With our highly vaccinated, and increasingly boosted, population here at MIT, shorter isolation periods may make even more sense for us,” Stuopis notes.

An important caveat is that none of these studies involved the Omicron variant. We don’t yet know for sure that infectiousness peaks at the same time with this variant or how vaccination affects the timeline for viral shedding. But we do know that the same precautions that have worked against earlier variants will continue to be effective, because it’s the same virus, and the mode of transmission has not changed.

The new guidelines mean that some people may leave isolation while they are still infectious, even if most transmission risk is gone after five days. “But that’s where that strict, five-day masking requirement comes in,” Stuopis stresses. “Wearing a well-fitted, highly filtering mask — like the KN95 or KF94 masks you can pick up at any Covid Pass drop-off site — any time you are around other people should reduce any remaining, post-isolation transmission risk significantly.”

Still, Stuopis expects MIT to continue recording high numbers of positive tests for the near future. “We now know that Omicron is a much more transmissible variant with a shorter incubation period,” she says. “With people testing positive three days after exposure, contact tracing is much less useful. Before you can be informed of a potential exposure, you may already have become infectious yourself, even if you haven’t yet tested positive or developed symptoms.”

The good(ish) news, everyone seems to agree, is that Omicron appears to cause milder illness, on average, than previous variants, particularly in vaccinated and boosted individuals. But while vaccines continue to be highly effective at preventing severe illness and hospitalization, it’s still important to take precautions against getting the virus and spreading it. “You probably didn’t end up in the hospital the last time you had a bad case of the flu,” Stuopis notes, “but it’s likely that you were extremely miserable for at least several days, maybe longer. A moderate breakthrough case of COVID-19 can feel as bad or worse, with symptoms that last even longer. And it’s important to remember that our families and communities include children who are too young to be vaccinated and other individuals who are at risk of serious outcomes if they become ill.”

The new guidelines are an attempt to strike that difficult balance between shielding the most vulnerable members of our community, preserving critical services at MIT and elsewhere, and avoiding stringent public health restrictions that result in more disruption than benefit. “There are no simple answers,” Stuopis says. “MIT will continue to make decisions based on the best scientific data available at any given time. Individuals in our community may choose to act more cautiously based on their own levels of risk tolerance or the vulnerability of family members. The most important thing — now and as we continue to live with this virus — is that we each take personal responsibility for protecting the health and safety of our communities in the best ways we can.”