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After SARS-CoV-2 infection, antibodies protect most health care workers against reinfection for up to 6 months, according to the results of the first prospective study of the subject.
Dr. David Eyre
The main message for health care workers is “if you had COVID, at least in the short term, you are unlikely to get it again,” said David Eyre, lead author, associate professor at the Big Data Institute and infectious disease clinician. University of Oxford, Oxford, United Kingdom Medscape medical news.
Eyre and colleagues evaluated the presence of two antibodies against SARS-CoV-2 among 12,541 health workers in the United Kingdom, including about 10% who had a history of polymerase chain reaction (PCR) – confirmed infection . Of these, 223 had no antibodies tested positive for PCR for the virus during the 31-week follow-up; two participants who did not have antibodies at baseline gave positive results.
The study was published online today in The New England Journal of Medicine.
Dr. Mark Slifka
“It’s great news because there have been so many questions about whether or not you can be protected against reinfection, and this study of health workers is really an elegant way to address this question,” he said. Mark Slifka, dr. Medscape medical news when asked to comment on the findings.
Although “there are millions of people in the United States who have been infected with COVID, we don’t know how common reinfection is,” said Slifka, a researcher at the National Primate Research Center in Oregon and a professor at the University of Health Sciences School of Medicine. from Oregon. , Portland, Oregon.
The probability of a positive PCR test result was 1.09 to 10,000 days at risk in those without antibodies, compared with 0.13 in 10,000 days in those with anti-peak antibodies.
Investigators also assessed the presence of anti-nucleocapsid IgG antibody titers. They found a significant upward trend in PCR-positive test results with increasing antibody levels. Similar to the findings of anti-peak antibodies, 226 of 11,543 healthcare providers who did not have anti-IgG nucleocapsid antibodies subsequently tested positive on PCR; instead, two of the 1,722 participants who did not have antibodies tested positive. Adjusted for age, sex and calendar time, this finding translates into an incidence rate ratio of 0.11 (0.13 per 10,000 days at risk; 95% CI, 0.03 – 0.45; P = .002).
“This is a study that some of us have tried to do,” said Christopher L. King, MD, PhD, professor of pathology and associate professor of medicine at Case Western Reserve University School of Medicine, Cleveland, Ohio.
“Let’s really follow a group like this longitudinally as they did, with a large population, and see such a big difference – it really confirms our suspicion that those who become infected and develop an antibody response are significantly protected. of reinfection.
“What’s great about this study is that it’s a nearly 10-fold reduction in risk if you’ve recovered from COVID and antibodies,” said King, who was not involved in the research. “That’s what many of us wanted to know.”
Unanswered questions remain
“We don’t know how long this immunity lasts,” King said. He predicted that antibody protection could last between a year and a year and a half. The duration of protection may vary. “We know that some people lose their antibodies pretty quickly, and others don’t,” he said.
Slifka said the suggestion of “a substantially reduced risk for at least 6 months … is great news, and the timing couldn’t be better because we’re launching vaccines.”
Interestingly, not all antibody responses are similar. For example, the data indicate that antibody levels after immunization with Pfizer / BioNTech or Moderna vaccines are higher on average than those of people who have had a natural infection, King said. He added that initial data on the developing AstraZeneca COVID-19 vaccine showed lower levels of antibodies compared to natural immunity.
Centers for Disease Control and Prevention recommend immunizing those with a history of infection. “People who have contracted COVID-19 can still benefit from their vaccination,” the CDC notes on its Facts About COVID-19 Vaccines website. “Due to the severe health risks associated with COVID-19 and the fact that re-infection with COVID-19 is possible, people may be advised to receive a COVID-19 vaccine even if they have had COVID-19 before,” the CDC said. .
The agency also notes that people appear to become susceptible to reinfection about 90 days after the onset of the infection. However, new evidence from the UK study that people with up to 6 months of immune protection could lead to altered recommendations, especially at a time when vaccine stocks are limited, Slifka said.
Another unanswered question is why the two participants in the antibody study subsequently tested positive for reinfection. “There are a lot of things that could have made these people more susceptible,” King said. For example, they may have been severely exposed to SARS-CoV-2 or may have been immunocompromised for some other reason.
Moreover, the immune response involves more than antibody levels, King noted. Research on rhesus monkeys suggests that T cells play a role, but not a role as prominent as antibodies. “What I think protects us from infection are primarily antibodies, although T cells are probably important. Once you get infected, T cells probably play a more important role in whether you get sick or not, ”he said. said.
Multiply + Add = More protected?
The 90% natural immunity protection in the study addresses the 95% efficacy associated with Pfizer and Moderna vaccines, Slifka noted. Even without immunization, this could mean that part of the US population is already protected against future infection.
Furthermore, the CDC estimates that there are approximately 7.7 cases of COVID-19 for each case reported.
As of September 30, the CDC reported that there were 6,891,764 confirmed cases. The agency estimates that, in general, about 53 million people in the United States have been infected. More recent figures from the Coronavirus Resource Center at Johns Hopkins University School of Medicine indicate that there have been 18.2 million cases in the United States since December 22nd. If this number is multiplied by 7.7, the total number protected could reach 140 million, Slifka said.
“This could really be a boost in terms of bringing down this pandemic in the next few months,” Slifka said.
“Now, if we were to change the current recommendations and briefly postpone the vaccination of people with COVID-19 confirmed cases until later, we could start achieving immunity to the herd fairly quickly,” he added.
Real life implications
“There is no 100% protection, even against the infection itself. So when you are dealing with someone with possible exposure to COVID-19, you still need to follow the proper precautions,” Slifka said.
However, he said: “This is great news for those on the front line who are wondering whether or not they would have protection if they had COVID-19 before. And the answer is yes – there is a very high chance of protection, based on this fairly comprehensive study. “
One limitation of the study is that the population consisted mainly of healthy adult health workers aged 65 or under. Further studies are needed to assess post-infection immunity in other populations, including children, older adults and people with coexisting conditions, including immunosuppression, the researchers note.
Eyre intends to continue monitoring the health workers in the study, some of whom were vaccinated for COVID-19. This ongoing research will allow him and coin researchers to “confirm the protection offered by vaccination and investigate how responses to post-vaccination antibodies vary depending on whether you have had COVID-19 before or not. We also want to understand more about how long post-infection immunity lasts. “
Eyre received grants as a member of the Robinson Foundation and as a senior member of the NIHR Oxford BRC during the study. Slifka and King do not report relevant financial relationships.
N Engl J Med. Published online December 23, 2020. Full text
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