There is evidence that having COVID-19 may not protect against infection again with some of the new variants. People may also have a second infection with previous versions of the coronavirus if they build up a weak defense the first time, new research suggests.
How long the immunity of a natural infection lasts is one of the big questions of the pandemic. Scientists still think reinfections are quite rare and generally less severe than the 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 had an earlier version of the virus.
In Brazil, several similar cases have been documented with a new variant there. Researchers are investigating whether reinfections help explain a recent increase in the city of Manaus, where three quarters of residents are believed to have already been infected.
In the United States, a study found that 10% of Navy recruits who had evidence of previous infection and repeatedly tested negative before starting basic training were infected again. That work was done before the new variants started to spread, said a study leader, Dr. Stuart Sealfon, of the Icahn School of Medicine at Mount Sinai in New York.
“The previous infection does not give you a free pass,” he said. “A substantial risk of reinfection remains.”
Re-infections represent a public health problem, not just a personal one. Even in cases where reinfection does not cause symptoms or only mild symptoms, people can still spread the virus. That is why health officials are recommending vaccination as a long-term solution and encouraging people to wear masks, keep physical distance and wash their hands frequently.
“It’s an incentive to do what we’ve always said: vaccinate as many people as possible and as quickly as possible,” said Dr. Anthony Fauci, the United States government’s leading infectious disease specialist.
“My analysis of the data suggests … and I want to underline suggests … protection induced by a vaccine may even be a little better” than natural infection, said Fauci.
South African doctors began to worry when they saw an increase in cases late last year in areas where blood tests suggested that many people already had the virus.
Until recently, all indications were “that the previous infection provides protection for at least nine months”, so a second wave should have been “relatively moderate”, said Dr. Shabir Madhi, from the University of Witwatersrand in Johannesburg.
Scientists have discovered a new version of the virus that is more contagious and less susceptible to certain treatments. It currently causes over 90% of new cases in South Africa and has spread to 40 countries, including the United States.
Madhi led a study testing the Novavax vaccine and found that it was 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 they were among those who did not.
“What this basically tells us, unfortunately, is that past infection with early 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 a similar concern and revealed a new variant that is also more contagious and less vulnerable to some treatments.
“Re-infection can be one of the drivers of these cases,” said Dr. Ester Sabino, from the University of São Paulo. She wrote an article in Lancet magazine about possible explanations. “We are still unable to define how often this is happening,” she said.
California scientists are also investigating whether a recently identified variant may be causing reinfections or an increase in cases there.
“We are analyzing 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-in-chief of the Journal of the American Medical Association, said he would soon present what he called “the Los Angeles variant”.
New variants were not responsible for the reinfections seen in the Marines study – this was done before the mutant viruses emerged, said Sealfon, who led the work with the Naval Medical Research Center. Other findings from the study were published in the New England Journal of Medicine; new ones about reinfection are published 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 starting basic training.
Among the 189 whose blood tests indicated they had been infected in the past, 19 tested positive again during the six weeks of training. This is much less than those without a previous infection – “almost half of them were infected at the basic training site,” said Sealfon.
The quantity and quality of antibodies that the previously infected Marines had on arrival were linked to the risk of catching the virus again. No reinfections have caused serious illness, but that does not mean that recruits were not at risk of spreading the infection to others, Sealfon said.
“It seems that reinfection is possible. I don’t think we fully understand why this happens and why immunity has not developed ”in these cases, said an immunology expert with no participation in the study, E. John Wherry, from the University of Pennsylvania.
“Natural infections can leave you with a range of immunity,” while vaccines consistently induce high levels of antibodies, Wherry said.
“I am optimistic that our vaccines are a little better.”
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