The latest found just 4.4 percent of people tested had detectable antibodies.
The study was published Monday by Imperial College London and Ipsos MORI, a market research company. The results showed the number of people with antibodies fell by 26.5 percent over the approximately three-month period. For health care workers, the rates stayed about the same.
More specifically, the study tested for detectable IgG antibodies. The researchers say it's still important, as a vaccine might provide better protection than the infection itself.
Researchers yesterday said the findings showed Britain was "a long long way" from anything approaching natural herd immunity.
Some infections, such as measles, cause what's known as sterilizing immunity.
"There are thousands of people who have that", said Dr. Igor Koralnik, chief of neuro-infectious disease at Northwestern Medicine in Chicago, who has already seen hundreds of survivors at a post-Covid clinic he leads.
With coronaviruses, scientists know less.
The research noted a reduction in people's immune response to Covid-19 over time.
The study has limits. The samples were not taken from the same people over and over again, but from different people over time.
Findings stemmed from finger prick tests, researchers said. Other studies have shown that different factors may impact how quickly antibodies decline. Age, co-morbidities, and the initial severity of illness all seem to play a role.
Derek Hill, a professor of medical imaging science at University College London, described the results as an "intriguing" but "inconclusive" piece of research into the effect coronavirus can have on the brain. "If someone tests positive for antibodies, they still need to follow national guidelines including social distancing measures, getting a swab test if they have symptoms and wearing face coverings where required", he added.
However, they said the findings suggested a significant rapid decline in immunity - raising the prospect that those infected could suffer repeatedly from infections in further waves. As with a cold, antibodies wane and people can get a cold a couple of times. Also as with a cold, people with robust immune systems, typically younger people, typically don't see as quick a drop in antibodies as with people with older immune systems. When a virus attacks, the body first produces IgM antibodies, which indicate active or recent infection.