Evidence is accumulating that having COVID-19 may not protect against re-infection with some of the new variants. People may also have second infections with earlier versions of the coronavirus if they mounted a weak defense the first time, new research suggests.
The duration of immunity against natural infection is one of the big questions of the pandemic. Scientists still think reinfections are quite rare and are usually less severe than initial ones, but recent developments around the world have raised concerns.
In South Africa, a vaccine study found new infections with a variant in 2% of people who previously had an earlier version of the virus.
In Brazil, several similar cases were documented with a new variant there. Researchers are exploring whether reinfections help explain a recent rise in the city of Manaus, where three-quarters of residents were believed to have been previously infected.
In the United States, one study found that 10% of marine recruits who had evidence of previous infection and had tested negative several times before starting basic training later became infected again. This work was done before the new variants began to spread, said a study leader, Dr. Stuart Sealfon of the Icahn School of Medicine in Mount Sinai, New York.
“Pre-infection doesn’t give you a free pass,” he said. “There remains a substantial risk of reinfection.”
Reinfections pose a public health problem, not just a personal one. Even in cases where reinfection does not cause symptoms or is only mild in nature, people may continue to spread the virus. That’s why health officials are urging vaccination as a longer-term solution and encouraging people to wear masks, maintain physical distance, and wash their hands frequently.
“It’s an incentive to do what we’ve been saying all along: vaccinate as many people as we can and do it as fast as we can,” said Dr. Anthony Fauci, the U.S. government’s top infectious disease expert.
“My look at the data suggests … and I want to emphasize suggests … vaccine-induced protection may even be a little better” than natural infection, Fauci said.
Doctors in South Africa began to worry when they saw an increase in cases late last year in areas where blood tests suggested many people had already had the virus.
Until recently, everything indicated that “the previous infection confers protection for at least nine months,” so a second wave should have been “relatively moderate,” said Dr. Shabir Madhi of the University of the Witwatersrand in Johannesburg.
Scientists have discovered a new version of the virus that is more contagious and less susceptible to certain treatments. It now causes more than 90% of new cases in South Africa and has spread to 40 countries, including the United States.
Madhi led a study that tested the Novavax vaccine and found it to be less effective against the new variant. The study also revealed that infections with the new variant were as common among people who had COVID-19 as those who did not.
“What it basically tells us, unfortunately, is that past infection with the first variants of the virus in South Africa does not protect” against the new one, he said.
In Brazil, an increase in hospitalizations in Manaus in January caused similar concerns and revealed a new variant that is also more contagious and less vulnerable to some treatments.
“Reinfection could be one of the drivers of these cases,” said Dr. Ester Sabino of the University of Sao Paulo. He wrote an article in Lancet magazine on possible explanations. “We haven’t yet been able to define how often this happens,” he said.
California scientists are also investigating whether a recently identified variant can cause reinfections or an increase in cases there.
“We’re looking at it now,” looking for blood samples from past cases, said Jasmine Plummer, a researcher at Cedars-Sinai Medical Center in Los Angeles.
Dr. Howard Bauchner, editor-in-chief of the Journal of the American Medical Association, said he would soon report on what he called “the Los Angeles variant.”
The new variants were not responsible for the reinfections observed in the Marine study: it was done before the mutated viruses appeared, said Sealfon, who led this work with the Naval Medical Research Center. Other findings from the study were published in the New England Journal of Medicine; news about reinfection are published on a research website.
The study included several thousand marine recruits who tested negative for the virus three times during a supervised military quarantine for two weeks before basic training began.
Of the 189 blood tests that indicated they had been infected in the past, 19 tested positive again during the six weeks of training. That’s a lot less than those without prior infection: “Nearly half of them became infected at the basic training site,” Sealfon said.
The quantity and quality of antibodies that Marines had infected prior to arrival was linked to the risk of contracting the virus again. Sealfon said no reinfection caused serious illness, but that doesn’t mean recruits aren’t at risk of infecting others.
“It seems that reinfection is possible. I don’t think we fully understand why this is so and why immunity has not been developed, ”said an immunology expert with no role in the study, E. John Wherry of the University of Pennsylvania.
“Natural infections can leave you with a wide variety of immunity,” while vaccines constantly induce high levels of antibodies, Wherry said.
“I’m optimistic our vaccines are a little better.”
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The Associated Press Health and Science Department is supported by the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.