Scientists Confirmed the First Covid-19 Reinfection in the U.S.

A Nevada man who recovered after an April infection tested positive again in May. Here’s what it all means.

Photo: Centers for Disease Control and Prevention via Unsplash

An enduring mystery about the coronavirus is how long immunity to the virus lasts, once a person recovers from an infection. While the hope was that immunity would last a long time, it’s becoming increasingly clear that protection from the virus fades and that reinfection is possible. Reports of reinfections in Hong Kong, the Netherlands, Belgium, and Ecuador have already been published during the pandemic. Now, a new case study in The Lancet confirms the first reinfection in the United States.

The paper, which was first published as a preprint at the end of August, follows the medical history of one man, a 25-year-old in Washoe County, Nevada, who tested positive for Covid-19 twice: first in mid-April, then again at the end of May. Two negative tests between his infections confirmed that he’d recovered from the initial illness. He had all the expected symptoms the first time around — sore throat, cough, headache, nausea, and diarrhea — and experienced them again during his second infection, together with low blood oxygen and shortness of breath.

While he recovered in self-isolation during his first infection, he had to be hospitalized the second time around. “The second infection,” the authors of the paper write, “was symptomatically more severe than the first.”

That’s not to say that reinfections are always more severe. The authors, led by bioinformaticist Richard L. Tillett, PhD, of the University of Nevada, say they can only speculate the reasons why the man’s illness was so bad the second time around: It could be that he got a much bigger dose of the coronavirus the second time he was infected. It’s possible that he was reinfected by a more virulent version of the virus (or one that was “more virulent in this patient’s context,” the authors note — a subtle distinction). Or it could be due to a phenomenon called “antibody-dependent enhancement,” in which virus particles latch onto certain antibodies, which makes it easier for them to infect host cells. For now, it’s unclear which is the case.

A genomic analysis of the samples showed that the viruses involved in each infection were genetically distinct, confirming that this is indeed a real reinfection, as opposed to a single lingering infection in which the virus inactivates and then reactivates. In the “highly unlikely” chance that the latter explanation is true, the authors write, SARS-CoV-2 would have to mutate in the body at a rate “that has not yet been recorded.”

So, what does this mean for the general public? It means that a person isn’t guaranteed total immunity if they were exposed to or infected with Covid-19 in the past. The major implication for vaccine development is that initial exposure to the virus “might not result in a level of immunity that is 100% protective for all individuals.” From a public health perspective, it means that everyone needs to take the same precautions to protect themselves from Covid-19 — whether they’ve been infected in the past or not.

In an accompanying commentary also published in The Lancet, Akiko Iwasaki, PhD, an expert on innate and adaptive immunity at the Yale University School of Medicine, outlines even more nuanced implications. Of note is the question of whether the fact that people can get reinfected by different strains of SARS-CoV-2 means we need a vaccine for each type. The short answer is, fortunately, no: “For now, one vaccine will be sufficient to confer protection against all circulating variants,” she writes, noting that the research on reinfection does not suggest the viral strain that causes the second infection is somehow better at dodging the immune system (a phenomenon called “immune evasion”). This suggests, in turn, that a different strain wouldn’t be any better at dodging the immune response triggered by a vaccine.

While the prospect of reinfection may seem alarming, the authors of the case study are careful to point out that one case study (or four, counting those from other countries) isn’t enough to establish the frequency of reinfection; in other words, “this event could be rare.” The reason it’s not understood how common this is, they write (rather pointedly), is because there’s an absence of genomic screening of positive cases in the United States and around the world.

“Certainly, limitations in screening and testing availability for SARS-CoV-2 exacerbate the poor surveillance efforts being undertaken not only to diagnose Covid-19 but also to obtain actionable genetic tracking of this agent,” they write.

Editor, Medium Coronavirus Blog. Senior editor at Future Human by OneZero. Previously: science at Inverse, genetics at NYU.

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