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Evidence is mounting that COVID-19 may not protect against new infection with some of the new variants. People can also get second infections with earlier versions of the coronavirus if they mount a weak defense the first time around, new research suggests.
One of the big questions of the pandemic is the duration of immunity against natural infection. Scientists still believe that re-infections are quite rare and usually less severe than the first 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 a previous version of the virus.
In Brazil, several similar cases have been documented with a new variant. Researchers are examining whether re-infections help explain a recent outbreak in the city of Manaus, where three-quarters of residents are believed to have been infected previously.
In the United States, a study found that 10% of marine recruits who had evidence of previous infection and who tested negative multiple times before starting basic training were subsequently re-infected. This work was done before the new variants began to spread, said study leader Dr Stuart Sealfon of the Icahn School of Medicine at Mount Sinai in New York City.
“A previous infection doesn’t give you a free pass,” he said. “A substantial risk of reinfection remains.”
Reinfection is a public health problem, not just a personal one. Even in cases where the reinfection causes no symptoms or only mild symptoms, people can still spread the virus. That’s why health officials recommend vaccination as a longer-term solution and encourage people to wear masks, keep a physical distance, and wash their hands frequently.
“It’s an incentive to do what we’ve been saying from the start: vaccinate as many people as possible and do it as quickly as possible,” said Dr. Anthony Fauci, the US government’s senior infectious disease specialist.
“My review of the data suggests … and I want to stress that … the protection induced by a vaccine may even be a little better” than natural infection, said Fauci.
Doctors in South Africa began to worry when they saw an upsurge in cases late last year in areas where blood tests suggested many people had already had the virus.
Until recently, all indications were “that the previous infection confers protection for at least nine months”, so a second wave should have been “relatively moderate,” Dr Shabir Madhi of the University of the Witwatersrand told Johannesburg.
Scientists have discovered a new version of the virus that is more contagious and less sensitive to certain treatments. It is responsible for more than 90% of new cases in South Africa and has spread to 40 countries including the United States.
Madhi conducted a study testing Novavax’s vaccine and found it to be less effective against the new variant. The study also found that infections with the new variant were just as common in people with COVID-19 as in those without.
“Basically what this tells us, unfortunately, is that the past infection with early variants of the virus in South Africa does not protect” against the new one, he said.
In Brazil, a spike in hospitalizations in Manaus in January caused similar concern and revealed a new variant that is also more contagious and less vulnerable to certain treatments.
“Reinfection could be one of the drivers of these cases,” said Dr Ester Sabino of the University of Sao Paulo. She wrote an article in the Lancet journal on the possible explanations. “We haven’t yet been able to define how often this happens,” she said.
Scientists in California are also studying whether a recently identified variant can cause re-infections or an increase in cases.
“We’re looking into this now,” looking for blood samples from previous cases, said Jasmine Plummer, a researcher at Cedars-Sinai Medical Center in Los Angeles.
Dr Howard Bauchner, editor of the Journal of the American Medical Association, said he would soon be reporting on what he called “the Los Angeles variant.”
The new variants weren’t responsible for the re-infections seen in the Marines study – this was done before the mutated viruses appeared, said Sealfon, who led this work with the Naval Medical Research Center. Further study results were published in the New England Journal of Medicine; news about the re-infection is posted on a research website.
The study involved several thousand Navy recruits who tested negative for the virus three times during a two-week supervised military quarantine before beginning basic training.
Of the 189 whose blood tests indicated they had been infected in the past, 19 tested positive again within six weeks of training. This is much less than those without a previous infection – “almost half of them got infected at the basic training site,” Sealfon said.
The quantity and quality of antibodies that previously infected Marines had when they arrived were related to their risk of contracting the virus again. No reinfection caused serious illness, but that doesn’t mean the recruits weren’t at risk of spreading the infection to others, Sealfon said.
“It seems that reinfection is possible. I don’t think we fully understand why and why immunity did not develop ”in these cases, said an expert in immunology without a role in the study, E. John Wherry of the University of Pennsylvania.
“Natural infections can leave you with a range of immunity” while vaccines routinely induce high levels of antibodies, Wherry said.
“I am optimistic that our vaccines are doing a little better.”
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The Associated Press’s Department of Health and Science receives support from the Department of Science Education at the Howard Hughes Medical Institute. The AP is solely responsible for all content.
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