If you get COVID-19 and you survive it, it's impossible to get it again — right? Wrong, according to a new study published in Clinical Infectious Diseases that suggests it's possible to contract COVID-19 twice. Right on the heels of that news came the first confirmed case of reinfection, in a man in Hong Kong. In the weeks since, three more reinfections have been reported across the U.S. and Europe.
Scientists aren't surprised that reinfection has reared its head. "Immunity to other coronaviruses is of variable duration and quality," Dr. John Sellick, D.O., professor of medicine in the Division of Infectious Diseases at the University of Buffalo, tells Bustle. "Reinfection is to be expected." While this isn't great news, it doesn't mean you should panic about getting coronavirus again.
How Does COVID-19 Infect You More Than Once?
The reinfection case in Hong Kong wasn't a case of catching the exact same virus twice. "The second encounter was with a slightly different variant of the SARS-CoV-2 virus, which was likely the result of a mutation," Dr. Robert Quigley M.D., regional medical director of risk mitigation company International SOS, tells Bustle. In other words, when scientists tested the genetic sequences of the viruses the man had caught, the second was different from the first.
What does this mean? "Viruses like SARS-CoV-2 are constantly mutating — it’s part of their life cycle," Dr. Quigley says. When you get a virus, your body will produce antibodies to fight it. Those antibodies will 'remember' that particular virus if it turns up again and protect you from getting sick. But if the virus changes, those antibodies might not help as much against its new form. This is why you need fresh flu vaccines every year; the flu constantly develops new strains, and last year's vaccine won't target this year's as well.
Mutations also sound scary, but they're not as bad as they seem. We know COVID-19 mutates "very slowly," Colin Furness Ph.D., assistant professor at the Dalla Lana School of Public Health at the University of Toronto, tells Bustle, though scientists will know more about that as they test out vaccines. And some mutations look like they're actually less serious than the original; one coronavirus variation found in Singapore, according to a study published in The Lancet, produced milder symptoms. Just because a virus mutates doesn't mean it turns into a Big Bad.
What Happens If Someone Gets COVID-19 Twice
"It seems that people who have had a very mild case of COVID, perhaps even an asymptomatic case, can probably be readily re-infected," Furness says. "If that happens, I would expect a mild case again, although there could be exceptions where a mild case might be followed by a severe case — we just don’t know yet." Some people, he says, may have already had COVID twice and not know about it, because they had no symptoms. The man in Hong Kong had no signs at all; his reinfection was diagnosed during routine airport testing.
Reinfection appears less likely if your first experience of COVID-19 was severe. "People who have a serious bout of COVID will generate antibodies and can expect to have immunity for some period of months or years, but we don’t yet know how long," Furness says. Research published by King's College London, which hasn't yet been peer-reviewed, found that people who were hospitalized with COVID-19 produced neutralizing antibodies that lasted for about three weeks, then started to decline two to three months afterwards. "Mild cases that resolve quickly will do so without significant production of antibodies, and for those cases, it looks like reinfection can happen. It might even be common," Furness says.
Fortunately, most cases of reinfection show a milder illness the second time around, Dr. Seema Sarin M.D., director of lifestyle medicine at EHE Health, tells Bustle. "Researchers are hopeful that this indicates that the immune system is working as it should to protect the body." This seems to be what happened in Hong Kong, Dr. Quigley says. The man was hospitalized for his first bout of the coronavirus, but when reinfected, he didn't feel ill, suggesting some antibodies may have done their job. "The encouraging news is that the patient likely developed immunity from the first exposure which was not enough to block reinfection, but enough to protect the patient from disease," he says. Right now, Dr. Sarin says, scientists don't know if people who've been reinfected and have no symptoms are even infectious.
What Does COVID-19 Reinfection Mean For Immunity Or A Vaccine?
There are still a lot of unknowns. "What we know about immunity and reinfection is increasing but still limited," Furness says. Dr. Sellick says we'll only begin to know more as time goes on, and other people become reinfected.
The one clear way to produce lasting immunity, Dr. Quigley says, is an effective vaccine that produces a strong antibody response, and that's not on the table yet. Right now, he says, you should keep wearing masks, social distancing, and using proper hygiene even if you've had COVID-19 once. Reinfection might not be the end of the world, but nobody wants to go through COVID-19 twice.
Colin Furness Ph.D.
Dr. Robert Quigley M.D.
Dr. Seema Sarin M.D.
Dr. John A. Sellick D.O.
Robbiani, D.F., Gaebler, C., Muecksch, F. et al. (2020) Convergent antibody responses to SARS-CoV-2 in convalescent individuals. Nature 584, 437–442. https://doi.org/10.1038/s41586-020-2456-9
Seow, J., Graham, C., Merrick, B., Acors, S. et al. (2020). Longitudinal evaluation and decline of antibody responses in SARS-CoV-2 infection. medRxiv. 10.1101/2020.07.09.20148429
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