People who have had 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 study of British health professionals concluded.
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 – can still 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, senior medical consultant at PHE 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 of acquiring an infection and passing it on to others.”
Main implications
Experts not directly involved in the research, known as the SIREN study, asked people to look at their main findings.
“This data reinforces the message that, for now, everyone is a potential source of infection for others and should behave accordingly,” said Eleanor Riley, professor of immunology and infectious diseases at the University of Edinburgh.
Simon Clarke, associate professor of cell microbiology at Reading University, said the study “has major implications for how we can get out of the current crisis.”
“This means that the vast majority of the population will need to have natural immunity or have been immunized in order to fully lift restrictions on our lives, unless we are prepared to see many more people being infected and dying from COVID-19,” he said.
PHE said in a statement that the study was unable to explore antibodies or other immune responses to the COVID-19 vaccines being launched in Britain. The effects of the vaccine will be studied as part of SIREN later this year, he said.
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 found 44 potential reinfections – two “likely” and 42 “possible” – among 6,614 participants who tested positive for antibodies. This represents an 83% protection rate against reinfection, they said.
The researchers said they would continue to monitor participants to see if this natural immunity could last for more than five months in some. But they said the first evidence from the next stage of the study suggests that some people with immunity may still have high levels of the virus.
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