After COVID infection, antibodies are highly protective for months

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After infection with SARS-CoV-2, the antibodies protect most health professionals from reinfection for up to 6 months, reveal the results of the subject’s first prospective study.

Dr. David Eyre

The main message for healthcare professionals is: “if you have had COVID, at least in the short term, you are unlikely to receive it again,” David Eyre, senior author, associate professor at the Big Data Institute and infectious disease clinic at the University from Oxford, Oxford, UK, said Medscape Medical News.

Eyre and colleagues assessed the presence of two antibodies to SARS-CoV-2 among 12,541 healthcare professionals in the UK, including about 10% who had a history of polymerase chain reaction (PCR) – confirmed infection. Of these, 223 who had no antibodies tested positive for PCR for the virus during 31 weeks of follow-up; two participants who had no antibodies at baseline tested positive.

The study was published online today in The new English medical journal.

Dr. Mark Slifka

“It’s great news because there have been so many questions about whether or not you can be protected from reinfection, and this health care study is really an elegant way to address that issue,” said Mark Slifka, PhD, Medscape Medical News when asked to comment on the findings.

Although “there are millions of people in the United States infected with COVID, we don’t know how common reinfection is,” said Slifka, a researcher at the Oregon National Primate Research Center and a 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-peak antibodies.

The researchers also assessed the presence of anti-nucleocapsid IgG antibody titers. They found a significant tendency to increase the results of positive tests for PCR with increasing levels of antibodies. Similar to the findings of anti-peak antibodies, 226 of the 11,543 health professionals who did not have IgG anti-nucleocapsid antibodies subsequently tested positive for PCR; in contrast, two of the 1172 participants who had no antibodies tested positive. Adjusted for age, sex and calendar time, this finding translates into an incidence rate of 0.11 (0.13 per 10,000 days at risk; 95% CI, 0.03 – 0.45; P = 0.002).

“This is a study that several of us have been trying to do,” said Christopher L. King, MD, PhD, professor of pathology and associate professor of medicine at Case Western Reserve University School of Medicine in Cleveland, Ohio.

“To really follow a group like this longitudinally like they did, with such 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 reinfection.

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

Unanswered questions remain

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

Slifka said the suggestion “a substantially reduced risk for at least 6 months … is great news, and the timing couldn’t be better, because we are launching vaccines”.

Interestingly, not all antibody responses are the same. For example, the data indicate that antibody levels after immunization with the 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.

The Center for Disease Control and Prevention recommends immunization for those with a history of infection. “People who fell ill with COVID-19 can still benefit from vaccination,” notes the CDC on its website Facts About Vaccines COVID-19. “Due to the serious health risks associated with COVID-19 and the fact that reinfection with COVID-19 is possible, people can be advised to get the COVID-19 vaccine, even if they have been sick with COVID-19 before” , the states of the CDC.

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

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 susceptible,” said King. For example, they may have been heavily exposed to SARS-CoV-2 or otherwise immunocompromised.

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 as antibodies. “What I think is protecting us from infection is mainly antibodies, although T cells are probably important. Once you are infected, T cells are likely to play a more important role in terms of getting very sick or not,” he said.

Multiplication + addition = more protected?

The 90% natural immunity protection in the study comes close to the 95% effectiveness associated with the Pfizer and Moderna vaccines, noted Slifka. Even without immunization, it could mean that a portion of the US population is already protected from future infections.

In addition, the CDC estimates that there are about 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, in all, approximately 53 million people in the United States were infected. More recent figures from the Coronavirus Resource Center at the Johns Hopkins University School of Medicine indicate that there were 18.2 million cases in the United States on December 22. If that count is multiplied by 7.7, the total protected number could reach 140 million, said Slifka.

“This could really be a boost in terms of overcoming this pandemic in the coming months,” said Slifka.

“Now, if we modify the current recommendations and briefly postpone vaccinating people with confirmed cases of COVID-19 until later, we can begin to achieve collective immunity very quickly,” he added.

Real-life implications

“There is no 100% protection, even against the infection itself. So when you’re dealing with someone with possible exposure to COVID-19, you still need to follow the appropriate precautions, ”said Slifka.

However, he said, “This is great news for those on the front lines who are wondering whether or not they would have any protection if they had COVID-19 before. And the answer is yes – there is a high chance that they will have protection. , based on this very broad study. “

A limitation of the study is that the population consisted predominantly of healthy adult health professionals aged 65 and under. “More studies are needed to assess post-infection immunity in other populations, including children, older adults and people with coexisting diseases, including immunosuppression,” the researchers note.

Eyre plans to continue to follow the study’s health professionals, some of whom were vaccinated against COVID-19. This ongoing research will allow him and his co-researchers to “confirm the protection offered by vaccination and investigate how post-vaccine antibody responses vary depending on whether you have had COVID-19 before or not. We also want to know more about how long post-infection immunity lasts. “

Eyre received grants as a Robinson Foundation fellow and a senior fellow at the NIHR Oxford BRC during the course of the study. Slifka and King do not report any relevant financial relationships.

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

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