The SIREN study examined the impact of infection on more than 20,000 healthcare workers from across the UK, and a pre-screening study found only 44 cases of reinfection among 6,614 people.
Two groups of people, one with no signs of previous infection and the other with signs of previous infection, were followed for up to six months.
The study – which has not yet been peer-reviewed – concluded that previous infection reduces the chances of getting the virus back by 83% for at least five months.
The cohort was tested regularly for Covid-19.
“About 6,000 of health workers were people who had evidence of having SARS-CoV-2 infection … and about 1
“The results suggest that reinfection rates in the positive cohort were 83% lower than the negative cohort during the follow-up period.”
However, researchers warned that the protection was not total and that it was unclear how long any immunity would last. It is also possible that those who have some immunity to the virus can still transmit it to others.
“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 the protection lasts,” said Susan Hopkins, senior medical adviser at PHE. and co-leader of the investigation, according to Reuters.
“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 may get an infection and transmit. (it) to others, “Hopkins said.
Hopkins emphasized the point during an interview with the BBC’s Today program on Thursday.
“[Infection] reduces your risk by at least 80% …. but that does not eliminate it, ”she said.
“We found people with very large amounts of virus in their nasal and throat swabs that would easily be within the range that would cause transmission levels to other individuals.” Hopkins stressed that people who had previously caught Covid-19 still needed to adhere to the rules of social distance to avoid transmitting the disease.
England is currently under a severe national lockdown after cases increased during the holiday period. The United Kingdom has registered more than 3.2 million cases of infection.
“What [the study] The real highlight is that immediately after infection you are likely to have a high level of protection, but it will decay over time, ”Niall Ferguson, a leading epidemiologist at Imperial College London, also told the BBC.
“Transmission is now slower than it would have been in the absence of people who became infected, and those people who have had the virus before are less likely to become infected – and that cumulatively slows down the spread.”
“This study supports the hypothesis that primary infection … confers a high degree of immunity to recurrence of infection in the short to medium term; with similar levels of symptomatic infection prevention as currently licensed vaccines for working age adults,” PHE report notes.
“Primary infection also reduces the risk of asymptomatic infection and thus further transmission; this is especially important in [that]… healthcare was considered a potential driver of ongoing community transmission in Wave 1 in the UK. “
The researchers will continue to investigate antibody responses to infection and the effect of Covid-19 vaccines.