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SAN DIEGO — Data from San Diego County suggest that few residents have gotten COVID-19 twice so far, echoing findings from researchers across the globe.
The Union-Tribune asked the County of San Diego Health and Human Services Agency for the number of people who’ve tested positive for the coronavirus twice, with their second test at least three months after their first. That cutoff is based on a Centers for Disease Control and Prevention report that an infected person can shed virus for up to three months after they first show symptoms
“Fewer than 10” San Diegans met those criteria, according to communications officer Sarah Sweeney.
That’s a tiny fraction of the more than 70,000 people who’ve tested positive for COVID-19 in the region. And Sweeney cautions that the county isn’t certain these are genuine cases of reinfection and not tests picking up remnants of a person’s first infection.
To figure that out, researchers would have to sequence viral samples from both tests and compare them. Clear genetic differences between the samples would be a strong sign that someone was infected twice.
That’s what scientists did to identify the first confirmed case of COVID-19 reinfection — a man living in Hong Kong who tested positive for the coronavirus (SARS-CoV-2) in late March and again in mid-August.
UC San Diego infectious disease expert Chip Schooley is the editor of the journal of Clinical Infectious Diseases, where the study published. He says it’s no surprise that researchers are finding instances of COVID-19 reinfection.
“We knew this would be the case,” Schooley said. “Other coronaviruses had the same experience: You develop immunity during a bout of infection, the immunity wanes and then the virus comes back around again and you get infected. And that’s what’s happening with this coronavirus as well.”
Local researchers say that’s not necessarily cause for concern.
Notably, the first person with a confirmed COVID-19 reinfection had mild symptoms during his first bout of disease and no symptoms the second time.
That’s reminiscent of a 1990 United Kingdom study in which volunteers were deliberately exposed to a coronavirus that causes the common cold. Most of the participants who were exposed twice still got infected again, but they didn’t develop symptoms or shed virus for as long as they did the first time — which presumably means they were less infectious.
“We don’t know whether that can be extrapolated to SARS-CoV-2, but that would be a good scenario,” said Alessandro Sette, a researcher at La Jolla Immunology.
Sette and colleagues recently looked at the immune responses of 185 people who recovered from COVID-19. Their study, which has not yet gone through scientific peer review, showed that most of these people’s immune responses were still detectable six to eight months after they got sick.
“We don’t see any ‘red flags,’ ” Sette said. “From what we’re seeing, it’s not hard to imagine that the response could last years.”
The findings fit with those of a study that tracked more than 12,000 U.K. health care workers from April to November. Workers with antibodies against the coronavirus, a sign they’d had COVID-19 before, were less likely to get infected than those who’d never been exposed before.
That suggests that antibodies, immune proteins that grab onto the surface of a virus and can prevent it from entering your cells, could reduce the likelihood and severity of reinfection. But not all antibodies block infection, and there’s evidence that T cells, which kill infected cells before they can spew out virus, also play a key role in fighting back the coronavirus.
Only time will tell how long immune responses to COVID-19 last — either due to natural infection or a vaccine.
An ideal vaccine would reduce your risk of reinfection for years, even decades. It would also limit your symptoms and make you less contagious if you get infected. But Sette says it’s too early to know how well a COVID-19 vaccine would do any of those things, and for how long.
“The prudent and responsible thing to do is to still adhere, to wear your mask and practice social distancing,” Sette said.
Another reason not to throw caution to the wind after recovering from COVID-19: Most people have not been exposed to the virus yet. So even if a second exposure doesn’t get you sick, you could spread the virus to someone who’s more vulnerable because they don’t have immunity.
At the moment, there’s a lot of viral spread going around.
“In terms of the most pressing issues today, it’s perhaps not as much reinfection as much as it is infections,” Sette said. “But clearly they do exist.”