COVID-19 survivors tend to have about a tenfold increase in protection against the virus, according to a government-funded study released Wednesday.
Why does it matter: There have been some documented cases of reinfection that worry survivors who do not gain any immunity. Although questions remain about how long or how long immunity lasts and what the impact of the variants will be, this large set of observational data supports the evidence that there is some protection.
The most recent: The study, published in JAMA Internal Medicine, examined commercial SARS-CoV-2 antibody testing data from 3.2 million patients in the United States as of January 1 and August 23, 2020.
- Of those who initially tested negative antibodies 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 initially antibody positive and were subsequently tested for active infection, they found that only 0.3% were positive for SARS-CoV-2 90 or more days later.
- “There is a tenfold decrease, which is essentially a 90% reduction in the risk for people who are antibody positive,” says Doug Lowy, co-author and deputy director of the National Cancer Institute, which conducted the study.
- “It’s been a long time coming, but our study is by far the largest study that looked at this, especially in the United States,” says Lowy.
Warning: Because the study examines the data in real time and was not conducted in a clinical trial setting, there could be “confounding factors” or distorting factors that affect the results, Lowy points out. This means that the tenth protection is an approximate average – in reality, “maybe it’s a difference of three times and maybe it’s a difference of twenty”.
- However, the results closely match another recent one NEJM a study in the UK that also found a difference of about ten times, he says.
What are they saying: Jennifer Juno, a senior researcher at the Doherty Institute at the University of Melbourne, who was not part of the study, says that “several studies now suggest that the previous infection does provide protection against reinfection, as we would expect.”
- “The key questions we need to address now include understanding the duration of this protection and the specific immune responses that are most strongly associated with protection,” she says.
Juno co-authored a different paper published last week in Communications about nature analyzing the level of antibodies in humans over a period of four months after infection. They found:
- People initially tend to have strong neutralizing antibodies that drop rapidly by about 50% in 55 days, but which also slow down the plateaus.
- And then other actors of the immune system rise. The level of B cells that produce antibodies to the spike coronavirus protein has increased over time in study participants, rather than decreased, says Juno.
- “This is encouraging news because it suggests that the immune system is generating a robust memory response to infection, which is likely to play a role in providing some protection against reinfection,” she added.
The whole picture: Vaccination is still highly recommended for those who have been infected before, say both Lowy and Juno.
- “Early studies suggest that people who have been previously infected have a substantial increase in antibody levels after receiving a dose of COVID vaccine, which indicates a great benefit from receiving the vaccine even if you have been previously infected,” says Juno.
Go deeper: The obstacles we face before reaching the herd’s immunity