By Kate Kelland
LONDON (Reuters) – People who have taken COVID-19 are highly likely to have immunity to it for at least five months, but there is evidence that those with antibodies may still be able to carry and spread the virus, a UK study of health professionals found.
Preliminary findings by scientists at Public Health England (PHE) showed that reinfections in people who have COVID-19 antibodies from a previous infection are rare – with only 44 cases found among 6,614 people previously infected in the study.
But experts warned that the findings mean that people who contracted the disease in the first wave of the pandemic in the first months of 2020 may now be vulnerable to contracting it again.
They also warned that people with so-called “natural immunity” – acquired from contracting the infection – may still be able to carry the SARS-CoV-2 coronavirus in their nose and throat, and may inadvertently transmit it.
“Now we know that most people who have had the virus and developed antibodies are protected against reinfection, but that is not total and we still don’t know how long the protection lasts,” said Susan Hopkins, PHE senior medical consultant and co-leader of the study, whose findings were published on Thursday.
“This means that even if you believe you have had the disease and are protected, you can be sure that it is highly unlikely that you will develop serious infections. But there is still a risk that you will get an infection and pass it on to others. “
A statement about the study said that its findings do not address antibody responses or other immune responses to vaccines that are now being launched against COVID-19, or about how effective the vaccines would be. Responses to vaccines will be considered later this year, he said.
The research, known as the SIREN study, involves tens of thousands of health professionals in Britain who have been tested regularly since June for new infections by COVID-19, as well as for the presence of antibodies.
Between June 18 and November 24, scientists detected 44 potential reinfections – two “likely” and 42 “possible” – in 6,614 participants who tested positive for antibodies. This represents an 83% protection rate against reinfection, they said.
The researchers plan to continue to monitor and evaluate participants to see if this natural immunity can last for more than five months in some. But they cautioned that initial evidence from the next stage of the study already suggests that some people with immunity can still carry high levels of the virus and pass it on to others.
“It is, therefore, crucial that everyone continues to follow the rules and stay at home, even if they have already had COVID-19,” they said in the statement on the results.
(Reporting by Kate Kelland; Editing by Mark Heinrich)