You Can Get COVID-19 Twice — What Does this Mean for Vaccine Development?

Photo by United Nations COVID-19 Response on Unsplash

The confirmed reinfection of a 25-year-old man in Nevada is one of a handful across the world. So far, the numbers are very low, but they have still caused panic in some quarters.

Does this mean we’ll have to socially isolate forever? Can we even have a vaccine?

Let’s unpack this for a bit.

The Case in Nevada

The specific case in Nevada is particularly worrisome. The patient is a 25-year-old man with no preexisting conditions. He caught COVID in April, which was confirmed by PCR, had a mild case and recovered.

Only 48 days later, he caught COVID again and this time he ended up in the hospital, although he did recover.

This may reflect a concern about antibody-dependent enhancement, which was seen in a few cases of SARS. Or he might have an underlying immune condition we didn’t know about. He was not serologically tested after the first infection, so his antibody levels were unknown. He did test positive for antibodies after the second.

Three other cases are reported in the Lancet article. One of them experienced worse infection, whilst the other two did not. One, in fact, was asymptomatic and only discovered because he happened to be tested at an airport. He was hospitalized as a precaution, but remained asymptomatic.

What is Antibody-Dependent Enhancement?

The big worry about the Nevada case (and also the Ecuador case, although fewer details are available) is that it may indicate something called antibody-dependent enhancement.

Consider dengue fever. This is a tropical disease carried by mosquitoes. There are four closely-related viruses that cause this unpleasant disease, which can sometimes result in hemorrhagic fever (which can be fatal). And the horrible thing is that the first time you catch dengue fever, it tends to be very mild. The second and subsequent times, it’s worse. Oh, and it doesn’t have a treatment. Or a good vaccine. There’s one for teenagers who have already had it which can prevent reinfection.

Antibody-dependent enhancement is the root cause behind how dengue fever seems to get worse in…