The SIREN study included thousands of UK health workers who were regularly tested on COVID-19.Credit: Kevin Coombs / Reuters
Most people who catch and recover COVID-19 are likely to be immune a few months later, a study found among more than 20,000 health workers in the UK.
The study – published on January 14 on the preprint server medRxiv – concluded that immune responses due to infection in the past reduce the risk of recapture of the virus for at least five months.
Over the past year, reports of recurrent infections with the SARS-CoV-2 coronavirus have shaken confidence in the immune system’s ability to maintain its defenses against the virus. Susan Hopkins, senior medical adviser at Public Health England and lead investigator of the study, told the interim results of the study, called SIREN, in a press conference. The data suggest that natural immunity may be just as effective as vaccination, she added, at least over the five-month period the study has covered so far.
The data indicate that recurrent infections are rare – they occur in less than 1% of approximately 6600 participants who were already ill with COVID-19. But the researchers also found that people who become infected again can carry high levels of the virus in their nose and throat, even if they do not show symptoms. Hopkins says such virus taxation carries a high risk of transmitting the virus to others.
“Re-infection is pretty uncommon, so that’s good news,” says immunologist John Wherry of the University of Philadelphia in Pennsylvania. “But you’re not free to run around without a mask.”
Regular inspection
SIREN is the largest study of coronavirus re-infection that has been systematically screened for asymptomatic infections, Hopkins said. Participants underwent blood tests every two to four weeks for SARS-CoV-2 antibodies and PCR tests for the virus itself.
Over the five months, the team found 44 possible reinfections. In the group of 14,000 participants who had not been infected before, 318 people tested positive for the virus.
Some of the re-infection cases are still being evaluated, Hopkins said. All 44 cases are considered ‘possible’ re-infections, and are classified on the basis of PCR tests combined with screening measures taken to reduce the risk of virus re-detection due to the initial infection. So far, only two of these 44 cases have passed more stringent tests. The study did not assess whether symptoms were better or worse during the second infection compared to the first, but Hopkins notes that only 30% of people with possible reinfections reported any symptoms, compared to 78% of participants with first infections.
At the moment, the team does not have enough data to bother who is at risk of re-infecting than others. And immunologist George Kassiotis of the Crick Institute in London notes that the participants in the study were mainly women and quite young. “This group is unlikely to experience the most severe form of COVID-19,” he says, “and may not be representative of the population as a whole.”
The study continues and researchers plan to collect data over a longer period of time, to realize how long immunity lasts and to understand the effects of a SARS-CoV-2 variant called B.1.1.7 that will emerge in 2020 has, to investigate. spread rapidly across the country. Although there are many reasons to suspect that existing protection should cover the new variants, it is possible that immune responses against one variant will be less effective against another, says Kassiotis. “It’s still an open question.”