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After the infection with SARS-CoV-2, antibodies protect most health workers from re-infection for up to 6 months, the results of the first prospective study on that topic reveal.
The main message to healthcare professionals is, “if you’ve had COVID at least in the short term, you’re unlikely to get it again,” David Eyre, senior author, associate professor at the Institute of Big Data and infectious disease clinician at Oxford University, Oxford, UK Medscape Medical News.
Eyre and colleagues estimated the presence of two antibodies to SARS-CoV-2 among 12,541 healthcare professionals in the UK, including about 10% of those with a history of confirmed polymerase chain reaction (PCR). Of these, 223 who did not have PCR-positive antibodies to the virus during the 31-week follow-up; two participants who had no antibodies at baseline were positive.
The study was published online today in New England Journal of Medicine.
“This is great news because there have been so many questions about whether you can protect yourself from re-infection or not, and this study by a healthcare professional is really an elegant way to address that issue,” said Dr. Mark Slifka for Medscape Medical News when asked to comment on the findings.
Although “there are millions of people in the United States who are 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 Oregon School of Health, Portland. , Oregon.
The probability of a positive PCR test result afterwards was 1.09 per 10,000 days of risk in those without antibodies, compared with 0.13 per 10,000 days in those who had anti-spike antibodies.
The researchers also assessed the presence of antibodies to nucleocapsid IgG antibodies. They found a significant trend to increase the results of PCR positive tests with increasing antibody levels. Similar to the findings of antibodies against spikes, 226 of 11,543 health care providers who did not have antibodies to nucleocapsid IgG were subsequently tested positive for PCR; in contrast, two of the 1172 participants who did not have antibodies tested positive. Adapted to age, sex, and calendar time, this finding translates to an incidence rate ratio of 0.11 (0.13 per 10,000 risk days; 95% CI, 0.03 – 0.45; Str = .002).
“This is a study that many of us have tried,” said Dr. Christopher L. King, Professor of Pathology and Associate Professor of Medicine at Case Western Reserve University School of Medicine, Cleveland, Ohio.
“Really follow longitudinally like this group 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 from re-infection.
“What’s great about this study is the almost 10-fold reduction in risk if you’ve recovered from COVID and have antibodies,” said King, who was not involved in the study. “That’s what many of us wanted to know.”
Questions remain unanswered
“We don’t know how long this immunity lasts,” 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 don’t,” he said.
Slifka said the suggestion of “significantly reduced risk in at least 6 months … is great news, and the weather couldn’t be better because we’re introducing vaccines.”
Interestingly, not all antibody responses are the same. For example, the data show that antibody levels after immunization with Pfizer / BioNTech or Moderna vaccines are on average higher than those in people who 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 immunization for those with a history of infection. “People who have contracted COVID-19 may continue to benefit from vaccination,” the CDC notes on its Facts About COVID-19 vaccines website. “Because of the serious health risks associated with COVID-19 and the fact that re-infection with COVID-19 is possible, people may be advised to receive the COVID-19 vaccine even if they have previously been ill with COVID-19,” the CDC states.
The agency also notes that people appear to be susceptible to re-infection approximately 90 days after the onset of infection. However, new evidence from a British study that people have up to 6 months of immune protection could lead to a modification of the recommendations, especially at a time when the supply of vaccines is limited, Slifka said.
Another unanswered question is why two study participants with antibodies were subsequently tested positive for reinfection. “There are a lot of things that could have made these people more sensitive,” King said. For example, they could be highly exposed to SARS-CoV-2 or be immunocompromised for another reason.
Furthermore, the immune response involves more than antibody levels, King noted. Research on rhesus monkeys suggests that T cells play a role, but not as prominent a role as antibodies. “What I think protects us from infection are primarily antibodies, although T cells are probably important. Once you become infected, T cells probably play a more important role in terms of whether you get very sick or not,” he said.
Multiplication + addition = More protected?
The protection of 90% of natural immunity in the study approaches 95% of the efficiency associated with the Pfizer and Moderna vaccines, Slifka noted. Even without immunization, it could mean that part of the American population is already protected from future infections.
Furthermore, the CDC estimates that there are approximately 7.7 COVID-19 cases for each reported case.
As of September 30, the CDC reported that there were 6,891,764 confirmed cases. The agency estimated that a total of 53 million people in the United States are infected. Recent data from Johns Hopkins University School of Medicine Resource Center indicate that there have been 18.2 million cases in the United States since December 22. If that amount is multiplied by 7.7, the total number of protected ones could approach 140 million, Slifka said.
“It could really be an incentive in terms of bringing down this pandemic in the next few months,” Slifka said.
“Now, if we could change the current recommendations and briefly postpone the vaccination of people with confirmed COVID-19 cases for later, we could start achieving herd immunity fairly quickly,” he added.
Real life implications
“There is no such thing as 100% protection, not even from the infection itself. So when you are dealing with someone who may be exposed to COVID-19, you still have to follow proper precautions,” Slifka said.
Regardless, he said, “This is great news for those on the front lines who are wondering whether or not they would have had protection had they had COVID-19 before. And the answer is yes – the chances are very high that they will have them protection, based on this rather large study. “
One limitation of the study is that the population consisted predominantly of healthy adult health workers over 65 years of age. “Further studies are needed to assess immunity after infection in other populations, including children, the elderly, and people with concomitant conditions, including immunosuppression,” the researchers note.
Eyre plans to continue monitoring health workers in the study, some of whom have been vaccinated against COVID-19. This ongoing research will allow him and investigators to “confirm the protection offered by vaccination and investigate how responses after the vaccine differ depending on whether you have had COVID-19 before or not. We also want to know more about how long postinfectious immunity lasts.”
Eyre received grants as a Robinson Foundation Fellow and a senior NIHR Oxford BRC Fellow during the study. Slifka and King did not report relevant financial relationships.
N Engl J Med. Published online December 23, 2020. Full text
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