New government-funded research this week should offer some comfort to people who have survived covid-19. This suggests that they have a low risk of coronavirus re-infection, at least about three months later.
Researchers at the National Cancer Institute, along with commercial testing laboratories and two companies, collected health care data for this study, published Wednesday in JAMA Internal Medicine.
They analyzed data from more than 3 million Americans who analyzed a commercial antibody test for SARS-CoV-2, the coronavirus that causes covid-19, between January and August 2020. Antibody tests, while not perfect, indicate or someone has recently had an infection. These people are divided on the basis of testing into those who have antibodies and those who do not. Then, the researchers looked at how many people in both groups later received a PCR test for covid-19, which is meant to diagnose an active infection.
About 10% of the people in each group underwent a PCR test. More people with antibodies were tested positive for the virus within the first 30 days after their antibody test than those without antibodies. But this is not surprising, as detectable traces of the virus can remain in the body for months, even after the symptoms have passed and the person is no longer contagious. It is therefore likely that these positive PCR results usually acquired the first infection. When the researchers looked specifically at the positive test count after the first month and especially more than 90 days later – enough time for a positive PCR test to probably indicate a true reinfection, the results were encouragingly different.
After three months or more, only 0.3% of people with an earlier positive antibody test tested positive for the coronavirus again, compared to 3% of those with a negative antibody test. In other words, an infection in the past was associated with a much lower risk of infection three or more months later.
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“People who have recovered from covid-19 should be reassured that antibody-positive is associated with some protection against a new infection,” said author Douglas Lowy, NCI’s deputy director general, in a statement. -pos said.
However, the findings come with their limitations. First, they cannot tell us exactly how much protection an infection will provide in the past against reinfection, or how long it will last (although other research suggested that it can be years). Another factor that this study cannot account for is the recent emergence of coronavirus variants. Some – like the one first identified in South Africa last year – will increase the risk of re-infection, as they may partially evade the immune response caused by an earlier infection or vaccination.
There is as yet no research showing that any variants that are currently spreading can completely evade the natural or vaccine-provided immunity. Our immune system has many weapons against a known germ, and most likely re-infections will appear to be softer than the first time.
Even before these new variants existed, there were documented cases of re-infection, including incidents where the symptoms were worse during the second time. And the findings of the new study still suggest that reinfection does occur, if rarely. So no one should assume that they are impermeable to covid-19 just because they survived a previous infection without problems. Ultimately, the best way is to keep everyone safe from covid-19 by vaccinating as many people as possible, including those who have already had the viral disease., according to Lowy. It is a remedy that carries far fewer risks than getting a natural infection.
“People who have recovered from covid-19 should still be planning to be vaccinated if they have the opportunity,” he said.
The NCI plans to continue funding research that will monitor the prevalence of reinfection in the general public, along with studies that will look at how our immune response to the virus may change over time and against new variants.