Survivors of COVID-19 tend to have an approximately ten-fold increase in protection against the virus, according to a government-funded study published on Wednesday.
Why it matters: There have been some documented cases of reinfection, leading to concerns that survivors will not obtain immunity. Although there are still doubts about how long or how long the immunity lasts and what the impact of the variants will be, this large set of observational data reinforces the evidence that there is some protection.
The most recently: The study, published in JAMA Internal Medicine, examined test data for commercial SARS-CoV-2 antibodies from 3.2 million patients in the U.S. from January 1 to August 23, 2020
- Among those who tested negative antibodies initially and were subsequently tested for active infection, they found that 3% were positive for SARS-CoV-2 90 or more days later.
- Of those who were positive for antibodies initially and were tested later for active infection, they found that only 0.3% were positive for SARS-CoV-2 90 or more days later.
- “There is a ten-fold decrease, which is essentially a 90% reduction in risk for people with positive antibodies,” said Doug Lowy, co-author and deputy director of the National Cancer Institute, who conducted the study.
- “It’s something that has been hypothesized for a long time, but our study is by far the largest study on this, especially in the United States,” says Lowy.
Embargo: Because the study examines data in real time and was not done in a clinical trial environment, there may be “confounding factors” or distortion factors that affect the results, Lowy points out. This means that the tenfold protection is an approximate average – in reality, “it may be a difference of three times and it may be a difference of twenty times”.
- However, the results closely match another NEJM UK study that also found a difference of approximately ten times, he says.
What they are saying: Jennifer Juno, a senior researcher at the Doherty Institute at the University of Melbourne, who was not part of the study, said that “several studies now suggest that the previous infection does offer protection against reinfection, as expected.”
- “The key issues that we need to address now include understanding the duration of that protection and the specific immune responses that are most strongly associated with protection,” she says.
Juno was co-author of another article published last week in Nature Communications observe the level of antibodies in people for a period of four months after infection. They found:
- People tend to have strong neutralizing antibodies initially, which decrease rapidly by about 50% in 55 days, but that decline decreases and stabilizes.
- And then other actors in the immune system come into play. The level of B cells that produce antibodies to the coronavirus spike protein increased over time in the study participants, rather than decreasing, says Juno.
- “This is encouraging news, as it suggests that the immune system is generating a robust memory response to the infection, which is likely to play a role in providing some protection against reinfection,” she adds.
The big picture: Vaccination is still highly recommended for those who have been infected before, say Lowy and Juno.
- “Early studies suggest that individuals who were previously infected show a substantial increase in their antibody levels after receiving a dose of the COVID vaccine, which points to a great benefit of receiving the vaccine, even if you have already been infected,” said Juno.
Go deeper: The obstacles we face before achieving collective immunity