Covid-19 antibodies may protect against further reinfection, study suggests

A study, published in the journal JAMA Internal Medicine on Wednesday, found that people who tested positive for Covid-19 antibodies had a lower risk of coronavirus infection compared to those who tested negative for antibodies.

“The study results are basically a 10-fold reduction, but I would have reservations about that. In other words, it could be an overestimate of the reduction. It could be an underestimation of the reduction,” said Dr. Douglas Lowy, deputy director of the National Cancer Institute, which was one of the authors of the study.

Lowy added that people who have recovered from Covid-19 should still be vaccinated when it is their turn.

The researchers – from the National Cancer Institute and LabCorp, Quest Diagnostics, Aetion Inc. and HealthVerity – examined data from more than 3.2 million people in the United States who completed a Covid-19 antibody test last year between January and August. Among those tested, 11.6% tested positive for Covid-19 antibodies and 88.3% tested negative.

In follow-up data, the researchers found that only 0.3% of those who tested positive for Covid-19 antibodies ended up testing positive for coronavirus infection later, after 90 days. Whereas, 3% of those with negative Covid-19 antibody test results were later diagnosed with coronavirus infection during the same period.

Overall, the study is observational and suggests that there is an association between positive Covid-19 antibody test results and a lower risk of infection about 90 days later – but more research is needed to determine a causal relationship and for how long protection against antibodies can last.

Lowy said more research is also needed to determine the risk of reinfection of one of the emerging variants of the coronavirus.

“Now that there are these variants of concern, what are the implications? The short answer is that we don’t know,” said Lowy. He also emphasized that people who test positive for antibodies should still be vaccinated against Covid-19.

It is already known that most patients recovering from Covid-19 have antibodies and reinfection seems to be rare so far – but it is still unclear for “how long the antibody protection will last because of the natural infection”, Dr. Mitchell Katz, from NYC The health system Health + Hospitals wrote in an editorial published along with the new study in JAMA Internal Medicine.

“For this reason, vaccination against SARS-CoV-2 is recommended regardless of antibody status,” wrote Katz. SARS-CoV-2 is the name of the coronavirus that causes Covid-19.

“How long the antibody protection provided by vaccines will last is also unknown,” he wrote. “Knowing how long protection with antibodies will last due to natural infection or vaccination is something that only time will tell.”