LONDON — People who have contracted the coronavirus are "highly unlikely" to contract the disease again for at least six months, according to a new Oxford study.
Researchers say the findings are "exciting" because they represent an important step in understanding how Covid-19 immunity may work.
The study, published Friday, claims to be the first large-scale research into how much protection people get against reinfection after contracting the coronavirus. It was part of a major collaboration between the University of Oxford and Oxford University Hospitals NHS Foundation Trust but has not yet been peer reviewed.
It comes after a string of encouraging vaccine results over the past couple of weeks following late-stage trial readouts from Pfizer-BioNTech and Moderna, as well as positive phase two results from AstraZeneca-Oxford.
There is growing optimism that a Covid vaccine could help bring an end to the coronavirus pandemic that has claimed over 1.3 million lives worldwide.
Public health officials and experts have warned it could take months, maybe even more than a year, to distribute enough doses of any prospective vaccine to achieve so-called herd immunity and suppress the virus.
The study covered a 30-week period between April and November with 12,180 health-care workers employed at Oxford University Hospitals.
The workers were tested for antibodies to the virus that causes Covid-19 as a way of detecting who had previously been infected. They were tested for the disease when they became unwell with symptoms and as part of regular testing.
The findings showed 89 of 11,052 staff without antibodies developed a new infection with symptoms. However, none of the 1,246 staff with antibodies developed a symptomatic infection. Staff with antibodies were also found to be less likely to test positive for the virus without symptoms.
"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.
In addition, researchers said the opposite also proved to be true. Health workers who did not have antibodies against Covid were found to be more likely to develop the infection.
Researchers said there was not yet enough data to make a judgment on protection from the initial infection beyond a six-month period. The study will continue to collect data, with the hope of verifying how long protection from reinfection can last.
"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 Oxford University Hospitals.
A previous study of staff at Oxford University Hospitals NHS Foundation Trust, published on Nov. 5, found antibodies to Covid-19 fell by half in less than 90 days.
That study, which has also not yet been peer reviewed, said antibody levels peak lower and fall faster in younger adults.
"We know from a previous study that antibody levels fall over time," Eyre said, referencing the research published earlier this month.
"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."