One of the enduring questions of the COVID-19 pandemic is how much immunity people have left after recovering from a coronavirus infection. New research suggests that the level of protection is comparable to vaccination – at least for a few months.
Among a group of hundreds of thousands of Americans who tested positive for a SARS-CoV-2 infection, the risk of developing a subsequent infection more than three months later was about 90% lower than for people who had not been infected before. was not and therefore according to researchers from the National Cancer Institute, no immunity to the virus.
In comparison, when the vaccines tested by Pfizer-BioNTech and Moderna in Phase 3 clinical trials, they reduce the risk of developing COVID-19 by at least 94%.
The findings, published Wednesday in JAMA Internal Medicine, could help inform plans to return workers to their offices, send students and teachers back to school campuses and reopen more economics.
‘I think we knew it, that immunity [after natural infection] long term, “said Dr. Monica Gandhi, an infectious disease specialist at UC San Francisco who was not involved in the new research.” But it’s still very exciting. “
There are three important things scientists need to know to understand the biological value of coronavirus antibodies, says Dr. Mitchell H. Katz, who heads the NYC Health and Hospitals. These are: Do antibodies protect against infection? Can they be reliably detected with current tests? And if they do provide protection, how long does it last?
The new study “provides reassuring answers to the first and second questions,” Katz wrote in an editorial accompanying the study.
To examine the immunity of coronavirus, the cancer researchers examined the results of more than 3 million blood tests administered to the Americans between the onset of the pandemic and August 23. A total of 378,606 of the tests were positive for SARS-CoV-2 antibodies – indicating that the person providing the sample had an active coronavirus infection.
Among the millions of people tested, some – about 11% of those who tested positive and 9.5% of those who tested negative – later took another test to look for evidence of the coronavirus’s genetic material in patient samples search. collected via the nose, throat or through saliva.
The researchers used these results to see if people who had a coronavirus infection were less likely to have SARS-CoV-2 particles in their system than their uninfected counterparts. For their analysis, they sorted the results into four groups based on the gap between the antibody test and the genetic test.
After performing the numbers, the researchers found that between 3% and 4% of those who originally tested negative for coronavirus antibodies later tested positive with the genetic test. This was true in all four intervals: 0 to 30 days, 31 to 60 days, 61 to 90 days, and more than 90 days. The stability was probably a reflection of the relatively stable rate at which people in their communities were infected at the time, the researchers said.
Compare this with the people who originally tested positive for coronavirus antibodies. Their genetic test results were positive in the first 30 days (11.3%) at a very high dose, which according to the researchers was probably a sign that the remaining viral particles are still being flushed out of their systems.
However, the positivity rate for the genetic test dropped to 2.7% in the second month after infection and to 1.1% in the third month. And after 90 days, only 0.3% of people with a coronavirus infection had another infection that was detected with a genetic test.
The coronavirus infection rate was ten times lower than for people who were presumably not previously infected.
It appears that the level of protection is comparable to the benefits that the Pfizer and Moderna vaccines offer in their clinical trials, the study authors pointed out.
‘Of course, protection induced by a safe vaccine is preferable,’ they added quickly, ‘as the population-wide risk of serious consequences of an authorized or approved vaccine is less great than that of natural infection. ”
Although the findings may be of great importance to scientists, they are unlikely to make much practical difference at the time of the pandemic, Gandhi said. This is because vaccines seem to be at least as protective as an infection in the past, and that they are already being rolled out.
These findings ‘could have been used two months ago’, she added.
While this study did not determine how long the benefits of a previous infection lasted longer than 90 days, other evidence suggests that it takes a while to diminish. Gandhi, for example, pointed to an article in Science that found that immune cells caused by SARS-CoV-2 stay in the body for at least eight months.
The findings may help explain why new infections have fallen in the province of Los Angeles following a devastating holiday. Dr. Roger Lewis, director of modeling COVID-19 hospitals for the LA County Department of Health Services, estimates that about 1 in 3 people in the country now have immunity to the coronavirus.
The authors of the study said that more research would be needed to get a clearer picture of the natural immunity against the coronavirus.
“Factors that influence the risk of re-infection – such as different virus strains, immune status of patients or other characteristics at patient level – should be evaluated in subsequent studies that include follow-up longer than 90 days,” they write.
This story originally appeared in the Los Angeles Times.