Can You Catch COVID-19 Twice?

Photo: fizkes, Shutterstock
Photo: fizkes, Shutterstock

You’re probably sick of hearing about the coronavirus, and it’s only existed on this earth for seven months or so — as far as we know. Can people get it twice? A recent case reported in Vox suggests the answer may be yes, but there are too many unknowns to confirm whether that’s true, or what it means. Here are a few things it’s important to keep in mind.

Test results aren’t perfect

First, how do we know if a person has gotten COVID twice? In this patient’s case, they were sick with COVID-like symptoms and got a positive test result; then they felt better and got two negative test results; then they got sick again and tested positive again.

These tests were all the PCR nose swab type (as opposed to antibody tests, which are different). This type of test is fairly accurate if it’s positive, but false negatives are fairly common. One study found that 21 days after symptoms began, 66% of patients had a false negative result.

So it’s possible (though unlikely) that the initial test was a false positive. It may also be the case that the patient had a single, long-term infection and the negative tests were false negatives. We know that some infections can last for months. Again, this isn’t super likely, but it’s definitely possible.

We need to know if these cases are rare or common

This Vox article is about one person. Let’s say that the test results were all accurate, and that the person definitely contracted two separate infections with the coronavirus. What does that mean for the rest of us?

Epidemiologist Marc Lipsitch tweeted that news stories like this make the mistake of “conflating ‘x is possible’ with ‘x is common.’” We don’t know yet if there’s something unusual about this person, or if cases like this are happening all over the world and not being detected.

For example, there are known cases of measles reinfection, but measles is recognised as a disease that, as a rule, you can only catch once. Its vaccine works well, and herd immunity is effective at limiting its spread. Those reinfection cases are rare blips that suck for the people involved, but they don’t change the overall picture of what is happening in the population as a whole.

Still, we recognise a trend by finding a case, and then another case, and then looking for more. Just a few months ago, we didn’t know if people could spread the coronavirus without showing symptoms. Now, we know that’s probably one of the major drivers of its spread.

Lots of important questions are still unanswered

Besides Did this person really get infected twice? and Is he the only one? there are many other important questions to which we still don’t have good answers. Scientists are working on them. They include:

  • Does infection only confer a short-term immunity that fades, like the coronaviruses that cause colds?
  • Do antibody tests accurately measure whether you are immune?
  • Can a vaccine confer long-term immunity, even if the virus itself doesn’t?
  • Is it possible that instead of protecting you, the first infection makes you more vulnerable to the second? (Another virus, dengue, works like this.)

We still have a long way to go before we give up on the idea of long-term immunity — or even short-term immunity. Even so, we know that natural herd immunity is not a saving grace, but a sign that we have failed to protect our society from the virus. Let’s hope for immunity, period, but let’s also hope that we get there with a vaccine and not by failing to protect each other.

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