High levels of antibodies have been found in almost all people infected with COVID-19 for at least six months, according to a major UK study.
The results showed that 99% of participants retained antibodies for three months.
Eighty-eight percent still had them after six months.
Scientists say the results should provide some reassurance that swift cases of reinfection will be rare.
Naomi Allen, a professor and chief scientist said at UK Biobank who conducted the study said that "Although we cannot be certain how this relates to immunity, the results suggest that people may be protected against subsequent infection for at least six months following natural infection."
On Wednesday a preprint study showed that just one shot of the Oxford AstraZeneca vaccine provided sustained protection for three months.
It showed a 76% efficacy until the second shot was given, and higher efficacy if the second dose was given at least 12 weeks after the first.
Health Secretary Matt Hancock used this to defend the country's vaccine roll-out strategy.
Britain has extended the gap between doses and given the shot to people of all ages, whereas France, Belgium, and Germany recommend that Oxford's vaccine is only given to under 65s.
Director of the Oxford Vaccine Group, Andrew Pollard said the study was also a success for reducing transmission:
"Well, that could have a really important impact in that it reduces the chances of someone who's exposed getting the infection, and if they don't get the infection, they can't pass it on. So it decreases the risk of transmission in the population."
The study's findings are only preliminary and still under review.
It may support Britain's decision to separate doses, but it did not give extra direct evidence of efficacy in older people.