LONDON (Reuters) – People who have had COVID-19 will most likely have immunity to it for at least five months, but there is some evidence that people with antibodies can still carry and spread the virus, a UK study of health professionals found.
Preliminary findings from Public Health England (PHE) scientists showed that re-infections in humans with 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 findings mean that people who contracted the disease during the first wave of the pandemic in the early months of 2020 may now be vulnerable to re-shelter.
They also warned that people with so-called “natural immunity” – acquired from having the infection – can carry the SARS-CoV-2 coronavirus in their nose and throat and pass it on unknowingly.
“We now know that most of those who have had the virus and developed antibodies are protected against reinfection, but this is not complete and we do not yet know how long the protection lasts,” said Susan Hopkins, senior medical advisor at PHE and co-leader of the study, the findings of which were published Thursday.
“This means that even if you think you’ve already had the disease and are protected, you can be assured that you are highly unlikely to get serious infections. But there is still a risk of getting an infection and passing (it) on to others. “
A statement on the study said the findings did not relate to antibodies or other immune responses to vaccines now being rolled out against COVID-19, or how effective vaccines would be. Responses to vaccinations will be considered later this year, he said.
The study, known as the SIREN study, involves tens of thousands of health workers in Britain who have been regularly tested for new COVID-19 infections and for the presence of antibodies since June.
Between June 18 and November 24, scientists discovered 44 possible re-infections – two “probable” and 42 “possible” – of the 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 assess the participants to see if this natural immunity can last longer than five months in some cases. But they cautioned that early evidence from the next phase of the study suggests that some people with immunity can still carry high levels of viruses 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 previously had COVID-19,” they said in the statement of their results.
Reporting by Kate Kelland; Editing by Mark Heinrich