A new UK study on Saturday suggests that individuals who have previously had Covid-19 are highly unlikely to contract the illness again for at least six months following their first infection.
The study, done as part of a major collaboration between the University of Oxford and Oxford University Hospitals (OUH) NHS Foundation Trust involving frontline healthcare workers, suggests that most people are unlikely to get Covid-19 again if they have already had it in the previous six months.
“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,” said Professor David Eyre of the University of Oxford's Nuffield Department of Population Health, one of the authors of the paper which is in pre-print stages.
“This ongoing study involving a large cohort of healthcare workers has shown that being infected with Covid-19 does offer protection against reinfection 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,” he said.
Prof Eyre explained that 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 the previous infection affects the severity of infection if people do get infected again,” he said.
Additionally, the opposite also proved true – healthcare workers who did not have antibodies against Covid-19 were more likely to develop the infection.
The latest study is part of a major ongoing staff testing programme supported by the NIHR Oxford Biomedical Research Centre and Public Health England and covered a 30-week period between April and November this year, with 12,180 healthcare workers employed at OUH.
“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,” said Dr Katie Jeffery, Director of Infection Prevention and Control for OUH.
The healthcare workers were tested for antibodies to the virus that causes Covid-19 as a way of detecting who had been infected before. The hospital tested staff regularly for Covid-19, both when they became unwell with symptoms and also as part of regular testing of well staff.
The researchers then followed whether staff who had been infected before had the same number of new Covid-19 infections as those who had not been infected before.
During the study, 89 of 11,052 staff without antibodies developed a new infection with symptoms. None of the 1,246 staff with antibodies developed a symptomatic infection.
Staff with antibodies were also less likely to test positive for Covid-19 without symptoms, 76 staff without antibodies tested positive compared to just 3 with antibodies. The three healthcare workers with antibodies who tested positive for the virus that causes Covid-19 were all well and did not develop symptoms of Covid-19 again.
Susan Hopkins, Deputy Director, National Infection Service, PHE and one of the study’s authors said: “This study is a fantastic example of how well-structured long-term cohort surveillance can produce hugely useful results.
"Studies like this one are absolutely vital in helping us to understand how this new virus behaves and what the implications are for acquired immunity.”
“Our comprehensive staff testing programme is revealing a regular stream of valuable information as we try to better understand how to tackle this disease,” added OUH Chief Executive Officer Dr Bruno Holthof.
Despite an estimated 51 million people infected with the virus worldwide, with high levels of transmission ongoing, reports of patients becoming re-infected after already having had Covid-19 remain rare. However, up until now, there have not been any large-scale studies of how much protection from reinfection people get after Covid-19.