On reinfection.

On reinfection.

If you’ve been reading about Covid-19 in the New York Times, you’ve probably learned that reinfection is very unlikely.

What you’ve learned is incorrect.

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Don’t get me wrong – I love the New York Times. Within the spectrum of United States politics, I am very far to the left. Anti-consumerist, prison abolitionist, environmentalist, feminist, climate activist, etc., etc. I fit into all those categories.

I’m also a scientist. I am staunchly pro-vaccine. I don’t like pesticides, but I’m a huge fan of GMO crops. (Honestly, I wish there was a category at the grocery store where you could pay to support genetically-modified organisms grown without environmental toxins – “organic” doesn’t have the nuance I’d like.)

So my goal here isn’t to rag on the New York Times. I’m including screenshots of their headlines only to give us a common frame of reference.

This is what the news is saying. And it’s wrong.

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It was going to be very difficult to demonstrate reinfection with Covid-19.

Why?

In general, reinfection with any virus will produce a milder illness the second time.

Most people’s first infection with Covid-19 is so mild that they don’t realize they have it – perhaps 80% of infections are “asymptomatic,” in which a person has been infected with the virus, is probably shedding the virus (thereby infecting other people), but feels totally fine. So, people’s second infection? Some percentage higher than 80% are likely to feel totally well, even though they might be shedding virus.

When people develop severe complications from Covid-19, the illness can linger for weeks or even months.

I don’t know for certain whether my family contracted Covid-19 in February, because there were no tests available here at the time. All I know is that we were two close contacts removed from someone who had just returned from China, that this close contact tested negative for influenza, that my family had been vaccinated for influenza, and that our symptoms precisely mirrored the common suite for Covid-19. But in any case, we felt horrible for about three weeks, and we experienced lingering fatigue with occasional coughing for about two months.

Lengthy recovery is so common that there’s a colloquial name for it: “long-haulers.” If we’re trying to identify whether someone was re-infected, we’d need to make sure that we weren’t looking at continued viral shedding during a lengthy recovery.

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To demonstrate that someone was re-infected with Covid-19, the following would have to happen:

  • A person gets tested for Covid-19 during their first infection.
  • The genome of the virus is sequenced after that first infection.
  • The person is re-infected.
  • The person happens to get a Covid-19 test during the second infection (even though it’s highly likely that this person feels well at the time).
  • The genome of the virus is sequenced after the second infection.
  • The genome of the virus that infected the person on the second occasion is noticeably different from the first (even though Covid-19 includes a proofreading enzyme that slows genetic drift).

That’s all very unlikely!

There are just so many coincidences involved – that you happen to get infected with an easily distinguishable virus the second time, that you happen to get a test the second time, that anyone took the (significant) trouble and expense to sequence both genomes.

And what I mean is, proving re-infection is very unlikely. Which is totally independent of the likelihood of re-infection itself.

And yet, even though it’s so unlikely we’d be able to prove that re-infection is occurring, we have.

We know, with 100% certainty, that people can be reinfected. We’ve documented it.

Given how unlikely it was that we’d be able to document reinfection, the fact that we’ve seen this at all indicates that it’s probably quite common. As you would expect based upon our bodies’ responses to other coronaviruses.

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Given that re-infection definitely occurs, and is probably quite common, why have you read that it’s unlikely?

The underlying probably is language usage. When my father – an infectious diseases specialist – talks about re-infection, he’s thinking about contracting severe symptoms during a second infection. Which is reasonable. He’s a medical doctor. He cares about helping sick people get better.

But when we’re thinking about how to respond, as a nation, to this pandemic, we’re thinking about the dynamics of transmission. We’re trying to answer questions like, “Can kids go to school without people dying?”

(Yup, they can! And should!)

From this perspective, we’re thinking about who is going to spread the virus, and where. We need to know whether a person who is protected from severe disease – either from prior recovery or vaccination – might shed viral particles. Will that individual register as a positive case on a PCR test? Will that individual get classmates or co-workers sick?

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Re-infections are probably the underlying cause of the current rise in cases in New York City.

70% or more of the population of New York City was infected with Covid-19 during April. That’s a huge percentage, well above what most researchers consider the “herd immunity threshold” for similar respiratory viruses.

For there to be another spike in cases now, many of those 70% would need to have lost their initial immunity. That’s also why you’d expect to see a higher “test positivity rate” – if many of the current cases are reinfections, then they’re likely to be milder. People with milder (or asymptomatic) infections are less likely to seek out a test.

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For general audiences, the phrasing I’d recommend is to say “Severe illness is unlikely during Covid-19 reinfections” as opposed to “Reinfection is unlikely.”

There have been a few cases of people’s second infection being more severe than the first, but these cases indeed appear to be quite rare.

But re-infection itself?

The fact that we’ve documented any instances of re-infection suggests that it’s quite common. Which we could have predicted from the beginning – indeed, I did. And that’s why I’ve been recommending – for months – policies very different from what we’ve done.