A large study of UK healthcare workers finds that immunity after coronavirus infection lasts for months, but those with antibodies may still be able to carry and spread the virus upon reexposure.
Immune responses from a previous SARS-CoV-2 infection reduce survivors’ risk of reinfection by more than 83 percent for at least five months, according to preliminary data from a study of more than 20,000 UK healthcare workers published by Public Health England. The researchers caution that people previously infected may still be able to transmit the virus.
“Overall I think this is good news,” Imperial College London epidemiologist Susan Hopkins, a senior medical adviser to Public Health England (PHE), tells The Guardian. “It allows people to feel that prior infection will protect them from future infections, but at the same time it is not complete protection, and therefore they still need to be careful when they are out and about.”
Between June and November last year, the researchers monitored, through monthly serological tests and PCR tests twice a month, the infection rates in those who had been infected with the virus before June and those who had not. They found 44 potential reinfections, including 13 symptomatic cases, among the 6,614 who’d had the virus before, and 318 cases among the 14,173 who had no evidence of past infection. The authors concluded from these results that prior exposure to SARS-CoV-2 provides 94 percent protection against symptomatic reinfection, and 75 percent protection against asymptomatic reinfection.
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The researchers also found that people who become reinfected can carry a high viral load in their noses and throats, even in asymptomatic cases, which correlates with a higher risk of spreading the virus to others, says Hopkins.