Risk of COVID-19 reinfection less than 1%, study finds

May 7 (UPI) — Less than 1% of people with COVID-19 will become reinfected with the virus within three months of recovery, according to an analysis published Friday by PLOS ONE.

Based on testing and retesting of more than 23,000 unvaccinated people with confirmed cases of the virus between March and July of last year, 0.04% of those infected once “experienced probable or possible recurrence,” the data showed.

Within six months of recovery from their initial illness, 4.3 cases of COVID-19 reinfection occurred for every 10,000 people infected with the virus, the researchers said.

“Fortunately, clinical COVID-19 recurrence was very uncommon within about four to six months of patients initial infection, especially less than 90 days from the initial COVID-19 episode,” study co-author Dr. Ithan Peltan told UPI in an email.

However, “unfortunately, reinfections will almost certainly be more common in un-vaccinated COVID-19 survivors beyond the six-month mark as natural immunity wanes and patients are exposed to COVID-19 variants,” said Peltan, a critical care specialist with Intermountain Healthcare in Murray, Utah.

Since the start of the pandemic, estimates regarding the risk for reinfection — or getting infected with the coronavirus again, likely with a different strain, after recovering from initial illness — have varied.

Some studies have suggested that those infected have immunity against the virus for at least three months, and that reinfection is extremely rare.

Still others have warned that older people may be at increased risk for reinfection due to their having weaker immune systems.

For this study, Peltan and his colleagues assessed more than 23,000 people with confirmed COVID-19 between March 11 and July 31, 2020, before vaccines against the coronavirus had been developed and distributed.

Of these patients, 122, or 0.5%, had a positive test result at least 60 days after recovery from initial infection, the researchers said.

However, only four of these patients were found to have “probable” COVID-19 recurrence, and all four exhibited symptoms, while three required a higher level of medical care compared to their initial diagnosis, the researchers said.

Six additional patients were determined to have “possible” reinfection, according to the researchers.

Within their study population, 90% of repeat positive COVID-19 tests “were not consistent with true recurrence,” they said.

Still, “vaccination is enormously important for patients with prior infection,” Peltan said.

“Natural immunity diminishes with time [and] vaccination will help patients gain durable protection from reinfection,” he said.


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