New government-funded research this week should provide some comfort to people who have survived covid-19. It suggests that they have a low risk of coronavirus reinfection at least about three months later.
Researchers at the National Cancer Institute teamed up with commercial testing labs and two health data collection companies for this study, published Wednesday in internal medicine JAMA.
They analyzed unidentified data from more than 3 million Americans who had been commercially tested for antibodies to SARS-CoV-2, the coronavirus that causes covid-19, sometime between January and August 2020. if anyone has had a previous infection. These people were divided into those who had antibodies and those who did not, based on testing. The researchers then looked at how many people in both groups subsequently received a PCR test for covid-19, which is intended to diagnose an active infection.
About 10% of people in each group passed a PCR test. More people with antibodies tested positive for the virus in the first 30 days after the antibody test than those without antibodies. But this is not surprising, because the detectable traces of the virus can remain in the body for months, even after the symptoms have passed and the person is no longer infectious. So, it is likely that these positive PCR results will usually detect the first infection. When the researchers specifically analyzed the positive test rate after the first month and especially more than 90 days later – long enough for a positive PCR test to likely indicate a true reinfection – the results were encouraging.
After three months or more, only 0.3% of people with a previous positive antibody test tested positive for coronavirus, compared with 3% of those with a negative antibody test. In other words, the past infection was linked to 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 being a positive antibody is associated with some protection against a new infection,” study author Douglas Lowy, NCI’s deputy chief executive, said in a statement. e-mail.
But the discoveries come with their limitations. First, they cannot tell us exactly how much protection a past infection will provide against reinfection or how long it will last (although other research has shown suggested that may be years). Another factor that this study cannot explain is the recent emergence of coronavirus variants. Some – like that identified first in South Africa last year – is believed to increase the risk of reinfection, as they may be able to partially avoid the immune response created by a previous infection or vaccination.
However, there is no research to show that any variant that is currently spreading can completely evade someone’s natural or vaccinated immunity. Our immune system has a lot of weapons against a familiar germ and most reinfections are likely to be milder than the first time.
Even before the emergence of these new variants, however, cases of reinfection have been documented, including cases if the symptoms were more severe in the second pass. And the findings of the new study still suggest that reinfection occurs, albeit rarely. So no one should assume that it is impervious to covid-19 just because they survived a previous infection without any problems. Finally, the best way to keep everyone safe from covid-19 is to vaccinate as many people as possible, including those who have already had the viral disease., according to Lowy. It is a remedy that involves a much lower risk than a natural infection.
“People who have recovered from covid-19 should continue to plan for vaccination when they have the opportunity,” he said.
NCI intends to continue funding research that will track 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.