Following COVID infection, antibodies are highly protective for several months

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Following infection with SARS-CoV-2, antibodies protect most healthcare professionals from reinfection for up to 6 months, the results of the first prospective study of the subject show.

Dr. David Eyre

The key message to healthcare professionals is, “if you’ve had COVID, at least in the short term, you’ll probably not get it again,” said David Eyre, senior author, associate professor at the Big Data Institute and Department of Infectious Diseases at Oxford University, Oxford, United Kingdom Medical news from Medscape.

Eyre and colleagues evaluated for the presence of two antibodies to SARS-CoV-2 among 12,541 healthcare professionals in the United Kingdom, including approx. 10% who had a previously confirmed polymerase chain reaction (PCR) infection. Of those, 223 who did not have antibodies tested positive for PCR for the virus during 31 weeks of follow-up; two participants who did not have antibodies at baseline tested positive.

The study was published online today in New England Journal of Medicine.

Dr. Mark Slifka

“This is good news because there have been so many questions about whether you can be protected from reinfection or not, and this health worker survey is really an elegant way to tackle this question,” said Mark Slifka, Ph.D. Medical news from Medscape when asked to comment on the results.

Although “there are millions of people in the United States who have been infected with COVID, we do not know how common reinfection is,” said Slifka, a researcher at the Oregon National Primate Research Center and professor at the Oregon Health Sciences University School of Medicine, Portland. Oregon.

The probability of a subsequent positive PCR test result was 1.09 per 10,000 days at risk among those without antibodies compared to 0.13 per. 10,000 days among those with anti-spike antibodies.

The investigators also assessed for the presence of anti-nucleocapsid IgG antibody titers. They found a significant tendency to increase PCR-positive test results with increasing antibody levels. Equivalent to Antibodies Found Antibodies 226 of 11,543 healthcare providers who did not have anti-nucleocapsid IgG antibodies were subsequently tested positive for PCR; in contrast, two of 1172 participants who did not have antibodies tested positive. Adjusted for age, sex, and calendar time, this finding translates to a 0.11 incidence rate (0.13 per 10,000 risk days; 95% CI, 0.03 – 0.45; P = .002).

“This is a study that a number 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.

“To really follow a group like this in the long run, as they have done, with a large population and to see such a big difference – it really confirms our suspicion that those who become infected and develop an antibody response are significantly protected against reinfection.

“What’s good about this study is that it’s almost a 10-fold reduction in risk if you’ve recovered from COVID and have antibodies,” said King, who was not involved in the research. “That’s what many of us have wanted to know.”

Unanswered questions remain

“How long this immunity lasts, we do not know,” King said. He predicted that antibody protection could last a year to a year and a half. The duration of protection may vary. “We know that some people lose their antibodies pretty quickly and others do not,” he said.

Slifka said the proposal for “a significantly reduced risk for at least 6 months … is good news and the timing could not be better because we are rolling out the vaccines.”

Interestingly, not all antibody responses are the same. For example, data indicate that antibody levels after immunization with the Pfizer / BioNTech or Moderna vaccines are, on average, higher than those that have had a natural infection, King said. He added that initial data on the evolving AstraZeneca COVID-19 vaccine showed lower antibody levels compared to natural immunity.

The Centers for Disease Control and Prevention recommends immunization for those with a history of infection. “People who have become ill with COVID-19 may still benefit from being vaccinated,” the CDC notes on its website about facts about COVID-19 vaccines. “Due to the serious health risks associated with COVID-19 and the fact that re-infection with COVID-19 is possible, people may be advised to get a COVID-19 vaccine even if they have previously been ill with COVID-19,” according to the CDC.

The agency also notes that people appear to be susceptible to reinfection approx. 90 days after the onset of infection. However, new evidence from the UK study that individuals have up to 6 months of immune protection may lead to a change in the recommendations, especially at a time when vaccine supply is limited, Slifka said.

Another unanswered question is why the two study participants with antibodies subsequently tested positive for reinfection. “There are many things that could have made these people more receptive,” King said. For example, they could have been highly exposed to SARS-CoV-2 or been immunocompromised for some other reason.

In addition, the immune response involves more than antibody levels, King noted. Research in rhesus monkeys suggests that T cells play a role, but not as prominent a role as antibodies. “What I think protects us from infection is primarily the antibodies, although the T cells are probably important. Once you are infected, the T cells are likely to play a more important role in whether or not you become very ill,” said he said.

Multiplication + addition = more protected?

The 90% natural immunity protection in the study approaches the 95% efficacy associated with the Pfizer and Moderna vaccines, Slifka noted. Even without immunization, this could mean that part of the U.S. population is already protected from future infection.

In addition, the CDC estimates that there are approx. 7.7 cases of COVID-19 for each reported case.

On September 30, the CDC reported that there were 6,891,764 confirmed cases. The agency estimated that a total of about 53 million people in the United States have been infected. Recent figures from the Johns Hopkins University School of Medicine’s Coronavirus Resource Center indicate that there were 18.2 million cases in the United States per year. December 22nd. If this number is multiplied by 7.7, the total protected number could approach 140 million, Slifka said.

“It could really be a boost in terms of beating down this pandemic in the next few months,” Slifka said.

“If we now change the current recommendations and briefly postpone vaccination of people with confirmed cases of COVID-19 until later, we could begin to achieve herd immunity fairly quickly,” he added.

Real effects

“There is no such thing as 100% protection, not even from 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.

Nevertheless, he said, “This is good news for those on the front lines who are wondering if they would have any protection or not if they had COVID-19 before. And the answer is yes – there is a very good chance of , that they get protection, based on this rather large study. “

One limitation of the study is that the population consisted predominantly of healthy adult health workers aged 65 or under. “Further studies are needed to assess immunity after infection in other populations, including children, elderly adults and people with coexisting conditions, including immunosuppression,” the researchers note.

Eyre plans to continue following the health personnel in the study, some of whom have been vaccinated against COVID-19. This ongoing research will allow him and coin researchers to “confirm the protection of vaccination and examine how antibody responses to vaccine vary according to whether you have had COVID-19 before or not. We will also understand more about how long immunity after infection lasts. . “

Eyre has received grants as a Robinson Foundation Fellow and NIHR Oxford BRC senior fellow during the conduct of the study. Slifka and King do not report any relevant financial matters.

N Engl J Med. Published online December 23, 2020. Full text

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