New government-funded research this week should offer some comfort to people who have survived COVID-19. It suggests they are at low risk of reinfection from the coronavirus, at least around three months later.
Researchers from the National Cancer Institute partnered with commercial testing laboratories and two healthcare data collection companies for this study. published Wednesday in JAMA Internal Medicine.
They analyzed unidentified data from more than 3 million Americans who had undergone a commercial antibody test for SARS-CoV-2, the coronavirus that causes covid-19, sometime between January and August 2020. The tests Antibody tests, although not perfect, indicate whether someone has had a recent previous infection. These people were divided into those with antibodies and those without, based on tests. The researchers then looked at how many people in both groups later underwent 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 tested positive for the virus within the first 30 days after their antibody test than those without antibodies. But that’s not surprising, since detectable traces of the virus can remain in the body for months, even after symptoms have passed and the person is no longer infectious. Therefore, it is likely that these positive PCR results have detected the first infection. When the researchers looked specifically at the rate of positive tests after the first month and especially more than 90 days after (enough time for a positive PCR test to likely indicate true reinfection) the results were encouragingly different.
After three months or more, only 0.3% of people with a previous positive antibody test tested positive for coronavirus again, compared to 3% of those with a negative antibody test. In other words, having a previous infection was associated with a much lower risk of infection three or more months later.
“People who have recovered from COVID-19 should rest assured that having positive antibodies is associated with some protection against re-infection,” study author Douglas Lowy, NCI’s senior deputy director, said in an email.
However, the findings come with their limitations. For one, they cannot tell us exactly how much protection a past infection will provide against reinfection, or how long it is expected to last (although other research has He suggested which may be years). Another factor that this study cannot take into account is the recent emergence of coronavirus variants. Some, like first identified in South Africa last year, they are believed to increase the risk of reinfection as they may partly evade the immune response created by a previous infection or vaccination.
Still, there is no research to show that currently spreading variants can completely evade natural or vaccine-provided immunity. Our immune system has many weapons against a known germ, and most reinfections are likely to turn out to be milder than the first time.
However, even before these new variants existed, cases of reinfection had been documented, including cases where the symptoms worsened in the second round. And the new study’s findings still suggest that reinfection does occur, albeit rarely. Therefore, no one should assume that you are impervious to covid-19 just because you survived a previous infection without problems. Ultimately, 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 much less risk than contracting a natural infection.
“People who have recovered from COVID-19 should plan to get vaccinated when they get the chance,” he said.
The NCI plans 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.