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Studying the Possibility of COVID-19 Reinfection

Research on nursing home cases suggests vaccines might be key to protect older immune systems from second infections

Nursing home worker helping woman with a walker. Both wearing face masks.

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En español | As news breaks about a virus strain in Brazil that appears to cause a reinfection of COVID-19, other reports of second infections, including those at a nursing home, are causing concern.

Those cases, at a skilled nursing facility in Kentucky, were detailed in a study released last week in the Centers for Disease Control and Prevention (CDC) Morbidity and Mortality Weekly Report (MMWR). Five of the nursing home's residents had two bouts of COVID-19 within three months. The second time around, their symptoms were more severe, and one resident died.

Reinfections within 90 days are rare, experts say. But they also note that immunity to the virus can decrease over time, and the risk of reinfection may differ among different people.

The report in the CDC's MMWR also noted that nursing home populations could have factors contributing to such reinfection and short-lived immunity, including older age, comorbidities and their close-quartered living environment.

The fact that the residents’ first infections were either asymptomatic or gave them only mild symptoms, and that they went on to have a more severe second bout of COVID-19, suggests that those initial infections didn't produce “a sufficiently robust immune response to prevent reinfection,” the authors wrote. Older age also tends to limit immune function, they note.

Widespread reinfections are not expected

Bruce Farber, M.D., chief of infectious diseases at Northwell Health in New York, says that the study, while alarming, is too small to convince anyone that such a “nightmare” of widespread reinfection “is going to affect chronic care settings in the future."

Alessandro Sette, a scientist with the Center for Infectious Disease and Vaccine Research, La Jolla Institute for Immunology, adds that it's important to focus on what these recent studies add up to mean.

"Of course you can get reinfected with COVID-19,” he says, echoing CDC advice that those who've had COVID-19 maintain strategies to reduce transmission risk, such as mask wearing and social distancing. But the question, says Sette, is “how often does it occur and what is the bigger picture coming out?”

The lack of scientific proof needed to zero in on the true reinfection rate is hindering scientists’ quest for answers, he says.

Vaccination can be key to eliminating hard-to-calculate risk

In order to prove that a patient has been reinfected with coronavirus, scientists need to show through PCR and antigen testing that a patient has been positive, then negative and then positive again for the virus. Enough such test results, with the genetic testing needed to analyze different strains of the virus involved, are hard to come by.

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Still, Sette believes cases of reinfection have been underestimated, and it's important, especially for people who are immunocompromised, to know the true infection rate.

For now, experts say vaccination can play a key role in building up immunity to prevent a first, or second, COVID-19 infection.

"Let's not play Russian roulette,” Sette says. “You should be vaccinated because you can't trust that you'll have strong enough immunity that you would be immune to reinfection."

Cheryl Platzman Weinstock is a contributing writer who covers health and science research and its impact on society. Her work has appeared in The New York Times and Kaiser Health News and on NPR.