By Kate Kelland
LONDON (Reuters) – People who have had COVID-19 are highly likely to have immunity to it for at least five months, but there are signs that those with antibodies may still be able to carry and spread the virus, a British study of health workers has found.
Preliminary findings from researchers 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 previously infected people in the study.
But experts warned that the results 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 catching it again.
They also warned that people with so-called “natural immunity”
“We now know that most of those who have had the virus and developed antibodies are protected against reinfection, but this is not total and we do not yet know how long the protection lasts,” said Susan Hopkins, senior medical advisor at PHE and co-chair of the study, the results of which were released Thursday.
“This means that even if you think you have already had the disease and are protected, you can be sure that it is very unlikely that you will develop serious infections. But there is still a risk that you could get an infection and transmit it to others. “
A statement from the study said its findings did not relate to antibody or other immune response to vaccines now being rolled out against COVID-19, or to how effective vaccines would be. Vaccine responses will be considered later in the year, it said.
The research, known as the SIREN study, involves tens of thousands of healthcare professionals in the UK who have been regularly tested since June for new COVID-19 infections as well as for the presence of antibodies.
Between June 18 and November 24, researchers discovered 44 potential reinfections – two “probable” and 42 “possible” – out of 6,614 participants who had tested positive for antibodies. This represents a protection rate of 83% against reinfection, they said.
The researchers plan to continue to monitor and assess participants to see if this natural immunity might last longer than five months in some. However, they warned that early evidence from the next phase of the study already suggests that some people with immunity may still carry high levels of the virus and could transmit it to others.
“It is therefore crucial that everyone continues to follow the rules and stays at home, even though they have previously had COVID-19,” they said in the statement of their results.
(Reporting by Kate Kelland; editing by Mark Heinrich)