12,180 health care workers employed at OUH were involved in the research.
Researchers at the University of Oxford and Oxford University Hospitals (OUH) NHS Foundation Trust have found that healthcare workers who tested positive for antibodies to Sars-Cov-2, the virus that causes Covid-19, did not develop symptoms of the disease again.
Professor David Eyre of the University of Oxford’s Nuffield Department of Population Health, said: “This ongoing study involving a large cohort of healthcare workers has shown that being infected with Covid-19 does offer protection against re-infection for most people for at least six months – we found no new symptomatic infections in any of the participants who had tested positive for antibodies, while 89 of those who had tested negative did contract the virus.
“This is really good news, because we can be confident that, at least in the short term, most people who get Covid-19 won’t get it again.
“We know from a previous study that antibody levels fall over time, but this latest study shows that there is some immunity in those who have been infected.
“We will continue to follow this cohort of staff carefully to see how long protection lasts and whether previous infection affects the severity of infection if people do get infected again.”
The study, which is yet to be peer-reviewed, covered a 30-week period – between April and November 2020 – where OUH staff were tested regularly for Covid-19 as well as antibodies to coronavirus.
During the study, 89 of 11,052 staff who did not have antibodies developed a new Covid-19 infection with symptoms.
The team also found that no-one among 1,246 healthcare workers with antibodies developed a symptomatic infection.
The researchers also said that those with antibodies were also less likely to test positive for Covid-19 without symptoms.
The team found that 76 staff without antibodies tested positive compared to just three with antibodies.
The three healthcare workers with antibodies who tested positive coronavirus were all well and did not develop symptoms of Covid-19 again, the researchers added.
This suggests that most people are unlikely to get Covid-19 again if they have already had it in the previous six months, they said.
Dr Katie Jeffery, director of infection prevention and control for Oxford University Hospitals, said: “This is an exciting finding, indicating that infection with the virus provides at least short-term protection from re-infection – this news comes in the same month as other encouraging news about Covid vaccines.”