The SIREN study looked at the impact of the infection on more than 20,000 healthcare volunteers across the UK, and a pre-print study found only 44 cases among 6,614 people.
Two groups of people, one with no history of previous infection and the other with evidence of past infection, were followed for up to six months.
The study – which has not yet been reviewed – concluded that past infection reduced the chances of catching the virus again by 83% in at least five months.
The cohort is tested regularly for Covid-19.
“About 6,000 healthcare workers are people who have evidence of SARS-CoV-2 infection … and about 14,000 healthcare professionals are people who have no evidence of previous SARS-CoV-2 infection. “Tom Wingfield, a senior clinical professor at the Liverpool School of Tropical Medicine, told the British Science Media Center.
“The findings show that the rates of re-infection in the positive cohort were 83% lower than in the negative cohort during the follow-up period.”
But researchers have warned that protection is incomplete and it is unclear how long immunity lasts. It is also possible that those who have some degree of immunity to the virus may still be able to pass it on 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 common and we still do not know how long the protection lasts,” said Susan Hopkins, senior medical adviser at PHE and co. leader of the study, Reuters said.
“Even if you believe you are already ill and protected, you can be sure that you are very unlikely to develop severe infections. But there is still a risk of contracting an infection and passing it on to others,” Hopkins said.
Hopkins highlighted the issue during an interview with the BBC Today program on Thursday.
“[Infection] reduces the risk by at least 80% … but does not eliminate it, “she said.
“We found people with very large amounts of the virus in the nasal and throat pads that would easily be in the range that would cause levels of transmission to other individuals.” Hopkins stressed that people who have previously caught Covid-19 still have to abide by the rules of social distancing to avoid transmitting the disease.
England is currently under a strict national blockade after cases increased during the holidays. The UK has registered more than 3.2 million cases of infection.
“What [the study] really emphasizes that you probably have a high level of protection right after the infection, but that will fall apart over time, “Niall Ferguson, a leading epidemiologist at Imperial College London, also told the BBC.
“Transmission is now slower than it would be in the absence of people who become infected, and those who have had the virus before are at lower risk of infection – and this cumulatively slows the spread.”
“This study supports the hypothesis that primary infection … provides a high degree of immunity against recurrent infection in the short and medium term; with similar levels of symptomatic infection prevention as current licensed vaccines for adults of working age,” PHE. reporting notes.
“Primary infection also reduces the risk of asymptomatic infection and thus further transmission; this is particularly important in [that]… healthcare is seen as a potential driver for continuous community transmission in Wave 1 in the UK. “
Researchers will continue to study the responses of antibodies to infection and the effects of Covid-19 vaccines.