Evidence is mounting that having COVID-19 may not protect against getting infected again with some of the new variants. People also can get second infections with earlier versions of the coronavirus if they mounted a weak defense the first time, new research suggests.
How long immunity lasts from natural infection is one of the big questions in the pandemic. Scientists still think reinfections are fairly rare and usually less serious 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 surge in the city of Manaus, where three-fourths of residents were thought to have been previously infected.
In the United States, a study found that 10% of Marine recruits who had evidence of prior infection and repeatedly tested negative before starting basic training were later infected again. That work was done before the new variants began to spread, said one study leader, Dr. Stuart Sealfon of the Icahn School of Medicine at Mount Sinai in New York.