Healthcare workers who have recovered from Covid-19 are largely protected against falling ill again for at least five months, a British study has found, but researchers warned some people could still carry and transmit the virus.
Healthcare workers are among those most exposed to the SARS-Cov-2 coronavirus, as countries across the world have grappled with waves of infections in the year since it first emerged.
Researchers from Public Health England’s SIREN study detected 44 potential reinfections out of 6,614 participants, who had already tested positive for antibodies in a five-month period between June and November 2020.
In their first published report – which has not yet been peer reviewed – the authors said this represents an 83% rate of protection from reinfection.
But they warned that although antibodies may confer some protection from becoming ill with Covid-19, early evidence from the next stage of the study suggests that some of these individuals carry high levels of virus and could continue to transmit it to others.
“This study has given us the clearest picture to date of the nature of antibody protection against Covid-19 but it is critical people do not misunderstand these early findings,” said lead author Susan Hopkins, senior medical adviser at Public Health England and the SIREN study lead.
“We now know that most of those who have had the virus, and developed antibodies, are protected from reinfection, but this is not total and we do not yet know how long protection lasts. Crucially, we believe people may still be able to pass the virus on.”
Getting it twice?
Independent experts welcomed the paper from the SIREN study, which has recruited almost 20,800 healthcare workers – including frontline clinical staff – to undergo regular testing to see if they have the virus or antibodies to show a past infection.
Danny Altmann, professor of immunology at Imperial College London and British Society for Immunology spokesman, said SIREN had collected a “really important” dataset of healthcare workers.
But he added it could be “disappointing to put hard numbers to the idea that immunity to this virus is seemingly so variable and feeble that there is a greater than one in 10 chance of suffering reinfection even at five months, let alone now, when many UK healthcare workers are more than nine months out from infections in the first wave”.
Julian Tang, honorary associate professor/clinical virologist at the University of Leicester, said the study suggests natural infection protection rates “are comparable to the current Covid-19 vaccines” adding that immunisation would likely boost natural immunity.
In December, a study published in the New England Journal of Medicine found that almost all healthcare workers studied in Oxford who had tested positive for antibodies were protected for at least six months.
Tang said hopefully these studies would “reduce the anxiety of many healthcare worker colleagues who have concerns about getting Covid-19 twice”.