If you are hearing about #covid19 “reinfections” in Asia, I can offer you my take as a virologist. The best explanation for what we’re seeing is likely due to three things...

1) The patients have likely indeed recovered from their covid infection and are on their way to clearing the virus as their immune system hunts down every infected cell and stray virion. But there are still lingering bits and pieces of the virus around.

2) these tests can be very sensitive at detecting viral genetic material, even it’s just a non-infectious byproduct of the immune system conquering the virus.

3) but it’s also sometimes the case that the test yields a false negative result; maybe the swab didn’t pick up enough material or was mishandled, so the next retest turning up positive could be catching the original infection, not a new one.

Any responsible coverage of these “reinfection” rumors makes the point that we should not assume that these recovered patients actually were reinfected again or even that the low levels of viral material detected means they are infectious to others.

For example, NPR writes “It is unclear whether they are infectious and why they tested positive after their earlier negative test.” https://www.npr.org/sections/goatsandsoda/2020/03/27/822407626/mystery-in-wuhan-recovered-coronavirus-patients-test-negative-then-positive

The main reason I’m skeptical that patients were actually reinfected so soon after recovering is due to what we know of the virus and recovery. Patients who beat their infection (and ~98-99% do), do so because their immune systems rev up enough to beat it.

And covid is barely mutating the parts that the immune system recognizes (the spike protein), so once a patient beats their high level of virus, they would easily be able to beat back whatever little virus they might get exposed to from others.

That’s how immunity works. Immunity can fade, but not on the scale on weeks that these reports suggest. Maybe after a year. So for now, these reports of “reinfections” are likely just an artifact of imperfect testing.

Covid-19 is a shock to all of us, but that doesn’t mean that it’s likely behaving radically differently from what we know of other viruses, even other coronaviruses. Odds are high there will be a simpler explanation soon if it’s not out there already (please send if you see one).