The SIREN research looked at the impact of the infection on more than 20,000 volunteer health workers across the UK and a pre-print of the study found only 44 cases out of 6,614 people.
Two groups of people, one without 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The study – which has not yet been peer reviewed – found that past infection reduced the chances of catching the virus again by 83% for at least five months.
The cohort has been tested regularly for Covid-19.
“The results suggest that reinfection rates in the positive cohort were 83% lower than in the negative cohort during the follow-up period. ”
But the researchers warned that protection was not complete and that the duration of immunity was unclear. It is also possible that those who have some degree of immunity to the virus can still pass it on to others.
“We now know that most of those who have had the virus, and developed antibodies, are protected against reinfection, but it is not total and we do not yet know how long the protection lasts”, Susan Hopkins, senior medical adviser at PHE and co-leader of the study, Reuters said.
“Even if you think you have had the disease before and are protected, you can be reassured that it is highly unlikely that you will develop serious infections. But there is always a risk that you could get an infection and pass it on to others, ”Hopkins said. .
Hopkins made this point during an interview with the BBC’s Today program on Thursday.
« [Infection] reduces your risk by at least 80%… but that doesn’t eliminate it, ”she says.
“We found people with very high amounts of the virus in their nasal and throat swabs that would easily be in the range that would cause levels of transmission to other people. Hopkins stressed that people who had previously caught Covid-19 still had to obey social distancing rules to avoid transmitting the disease.
England is currently under strict national lockdown after cases surged during the holiday period. The UK has recorded more than 3.2 million cases of infection.
“What [the study] What really stands out is that immediately after infection you probably have a high level of protection, but that will deteriorate over time, ”also told the BBC Niall Ferguson, a leading epidemiologist at Imperial College London.
“Transmission is now slower than it would have been in the absence of infected people and people who have already been infected with the virus are less likely to be infected – and this slows the spread. ”
“This study supports the hypothesis that primary infection… provides a high degree of immunity against repeated infection in the short to medium term; with similar levels of prevention of symptomatic infection as currently licensed vaccines for working-age adults ” report notes.
“Primary infection also reduces the risk of asymptomatic infection and therefore subsequent transmission; this is particularly important [that]… Health care was seen as a potential driver of continued community transmission during Wave 1 in the UK. ”
Researchers will continue to study antibody responses to infection and the impact of Covid-19 vaccines.