Thursday, September 10, 2020

COVID-19 Reinfections: Many Questions to be Answered

Environmental & Science Education, STEM, Health, Medicine

Edward Hessler

The report of a confirmed case of a COVID-19 reinfection in the United States came as a surprise. The most notable, attention-getting feature of the re-infection of a 25-year old, Reno, Nevada male was that the second infection turned out to be more serious than the first. The expectation was that when re-infection occurs a less severe bout would follow.

In an information brief for STAT, Andrew Joseph notes some things to look for in assessing reports as they make their way from the scientific literature to the media.

--First, the Nevada case. Forty-eight days after testing negative twice the symptoms he had experienced returned--sore throat, cough, headache, nausea and diarrhea--and he had to be hospitalized (pneumonia). "[V]irus samples from both of his infections...were different, providing evidence that this was a new infection distinct from the first."

--Immunity. Our "immune response...creates memories of the virus" which as is the case of "other corona thought to (provide protection) "to last for perhaps a little less than a year to about three years." SARS-CoV-2 is new it is not known how long immunity will last, "what mechanisms provide protection, and "what levels of (blood indicators) are required to signal that someone is protected."

--Experts expect second cases to be milder. Why? "[T]his is what happens with other respiratory pathogens." There was a case in of re-infection in Hong Kong but it was asymptomatic, detected only after a mandatory sample following a flight. The Reno case is a perplexing counterexample.

--What level of immune response did both cases generate. No antibodies could be detected following the first infection of the man in Hong Kong. The Nevada man was not tested following his first infection. Immune responses vary and Sarah Cobey at the University of Chicago told Joseph, that "'Infection is not some binary event. There's going to be some viral replication, but the question is how much is the immune system getting engaged." Currently "it's thought that more than 20%

--The big question. Are those who are re-infected a second time infectious. It is not known but if it turns out that they are not spreaders "that's obviously good news."

--Another big question. People will become broadly susceptible again but by that time any protection from a first infection is expected to be much weaker. With "the arrival of a vaccine and broad uptake of it, that could change the dynamics of local outbreaks," leading to what is known as "herd immunity," the point "when enough people are immune that transmission doesn't occur." It is thought but not known that "more than 20% of residents (in some communities) have experienced an initial Covid-19 case, and are thus theoretically protected from another case for some time. This is below the standard of herd immunity, though. However, transmission risk could be increased "if more people become susceptible again.

Whether the Reno case is a one-off or generalizable is not known although modelers are starting to include this as a factor "into their forecasts."

Harvard epidemiologist Michael Mina told Joseph that “'There are millions and millions of cases. The real question that should get the most focus, Mina said, is, What happens to most people?'” (My emphasis) This is an important question.  The media love storieslike these...waning antibodies and re-infection based on "onesies" and "twosies" or even on anecdotes.  The evidence suggests that people are likely to develop immunity of some kind to COVID-19 and it is this immunity we need to know more about: how long, how strong, what effects, etc.

Joseph's full brief made be read here

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