I hear there has been a confirmed case of SARS-CoV-2 re-infection in Hong Kong?! How worried should I be?

Biology/Immunity Infection and Spread

A: Not very.

In the words of immunologist Dr. Akiko Iwasaki, “This is no cause for alarm – this is a textbook example of how immunity should work.”

What do we know? In a press release yesterday, researchers described the first confirmed case of re-infection in a 33-year old Hong Kong man returning from Spain.

How do we know this was a new infection? The genetic signature of the second infection was slightly different from the first infection, providing strong evidence for separate infections rather than a relapse of the same infection.

The patient was infected with SARS-CoV-2 four months prior in Hong Kong with mild symptoms. He then tested positive upon re-entry into Hong Kong from Spain but with no symptoms.

So WHY is this not cause for alarm?

• The second infection was asymptomatic, so while immunity didn’t block detectable infection, it protected from disease.

• The individual had no detectable antibodies after his first infection, while most COVID-19 patients DO mount an antibody response after infection.

• The individual did produce antibodies after the second exposure, consistent with the immune system eliciting a stronger response with repeated exposures (like a booster shot from a vaccine).

• This is one case out of millions of confirmed COVID-19 cases, so we don’t know if this is a rare event or something that will be the norm.

What questions does this raise?

• Even with no symptoms, a re-infected person *may* be able to spread the infection to others, but the extent and duration of infectiousness compared to first infections is currently not known.

• Since herd immunity relies on immune people *not* being able to infect others, this bolsters the consensus that the only safe and effective way to achieve herd immunity is through vaccination.

• Recovered COVID-19 patients will also likely need to be vaccinated, and should also continue to take standard precautions to prevent transmission to others.

Bottom line: KEEP CALM–in science ONE case never tells the whole story.

But watch this space for updates on the overall body of evidence regarding re-infection and immunity.

The Nerdy Girls

Dr. Iwasaki’s excellent thread with immune system visuals

News coverage of the findings:

New York Times  


Great new piece on potential types of immunity for SARS-CoV-2