Survivors of COVID-19 tend to have protection against the virus about tenfold, according to a government-funded study published Wednesday.
Why it matters: There have been some documented cases of reinfection that have raised concerns that survivors will not receive immunity. While questions remain about how long or how long immunity lasts and what the impact of variants will be, this large set of observational data supports evidence that there is some protection.
The last: The study, published in JAMA Internal Medicine, examined commercial SARS-CoV-2 antibody test data from 3.2 million US patients from January 1 to August 23, 2020.
- Of those who initially tested antibody negative and later tested for active infection, they found that 3% were positive for SARS-CoV-2 for 90 days or more.
- Of those who were initially antibody positive and later tested for active infection, they found that only 0.3% were positive for SARS-CoV-2 for 90 days or more.
- “There’s a tenfold increase, which is essentially a 90 percent reduction in the risk for people who are positive for antibodies,” said Doug Lowy, co-author and deputy director of the National Cancer Institute, who conducted the study.
- “It’s something that has long been assumed, but our study is by far the largest study to look at this, especially in the United States,” says Lowy.
Caveat: Because the study examines real-time data and was not done in a clinical trial setting, there may be “confounding factors” or confounding factors that influence the results, Lowy points out. This means that the ten-fold protection is a rough average – in fact, “maybe it’s a three-fold difference, and maybe it’s a twenty-fold difference.”
- However, the results are very similar to another recent one NEJM study from the UK that also found about a ten-fold difference, he says.
What they say: Jennifer Juno, a senior research fellow at the Doherty Institute at the University of Melbourne who was not part of the study, says, “Several studies now suggest that previous infection does indeed protect against reinfection, as we would expect.”
- “The most important questions to answer now include understanding the duration of this protection and the specific immune responses most strongly associated with protection,” she says.
Juno co-authored another article published last week in Nature Communications looking at the level of antibodies in humans over a period of four months after infection. They found:
- People often initially have strong neutralizing antibodies that decrease rapidly by about 50% within 55 days, but that decline slows and plateaus.
- And then other actors of the immune system absorb it. The level of B cells that produce antibodies to the coronavirus spike protein increased over time in their study participants, instead of decreasing, Juno says.
- “This is encouraging news as it suggests that the immune system is generating a robust memory response to infection that will likely play a role in providing some protection against reinfection,” she adds.
The big picture: Vaccination is still highly recommended for those previously infected, both Lowy and Juno say.
- “Early studies suggest that subjects who were previously infected show a significant increase in their antibody levels after receiving one dose of a COVID vaccine, indicating a great benefit from getting the vaccine, even if you have been previously infected” , says Juno.
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