In a new study from Fornaroli Hospital in Magenta, Italy, researchers found that reinfection after recovery from COVID-19 infection is very rare, and immunity in former patients could be long-lasting.
They found natural immunity to SARS-CoV-2 appears to confer a protective effect for at least a year, which is similar to the protection reported in recent vaccine studies.
In the study, the team analyzed the health records of more than 15,000 people. Nearly 13,000 had tested negative for COVID-19 on their initial tests, while 1,579 had tested positive.
Reinfection was defined as the occurrence of a new infection at least 90 days after “complete resolution of the first infection,” to make sure there was no confusion about traces of the first infection lingering in tests.
Within about a year afterward, 3.9% of people who’d never tested positive for COVID-19 in prior testing did acquire a COVID infection.
In contrast, just 0.31%—five people—of those who’d previously been infected picked up a second bout of the illness.
Four of the five patients either worked in or visited hospitals, the researchers noted, suggesting that they had especially high potential exposures to the virus.
Only 1 in 5 reinfected patients was sick enough to require hospitalization.
What’s more, reinfection typically occurred only after much time had elapsed: The average time from initial infection to reinfection was 230 days.
The team stressed that none of this means the previously infected should skip COVID-19 vaccination.
Achieving herd immunity through natural infection is a long and painful process and, historically, the only human disease to be eradicated, smallpox, was eradicated through vaccination, not a natural infection.
If you care about COVID-19, please read studies about the cause and treatment for heart damage in COVID-19 and findings of single Pfizer COVID-19 vaccine 90% effective after 21 days.
For more information about COVID-19 prevention and treatment, please see recent studies about these blood thinning drugs may lower death risk in COVID-19 patients and results showing that cholesterol-lowering drugs may help people survive severe COVID-19.
The study is published in JAMA Internal Medicine. One author of the study is Dr. Nicola Mumoli.
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