Findings from the largest antibody testing programme in the country suggests that our antibody response to Covid-19 reduces over time after infection.
Over 365,000 randomly selected adults tested themselves at home using a finger prick test between June 20 and 28 September to check if they had antibodies against Covid-19.
During this time period, the proportion of people who tested positive for antibodies declined by 26.5 per cent.
Researchers say this suggests that antibodies reduce in the weeks or months after a person is infected with the virus.
The study was conducted by Imperial College London and Ipsos MORI, and is the largest Covid-19 antibody testing programme so far.
The results of all three rounds of antibody testing indicate that the first wave of the pandemic occurred over a relatively short period in March and April.
There was a steep decline in the proportion of people who reported having symptoms and who tested positive for antibodies from early April, two weeks after national lockdown.
The results suggest that people who did not show symptoms of Covid-19 are likely to lose detectable antibodies sooner than those who did, scientists say.
The findings also show the loss of antibodies was slower in 18 to 24 year-olds compared to those aged 75 and over.
Health Minister Lord Bethell said: "This study led by Imperial and Ipsos MORI is a critical piece of research, helping us to understand the nature of COVID-19 antibodies over time, and improve our understanding about the virus itself.
"We rely on this kind of important research to inform our continued response to the disease, so we can continue to take the right action at the right time.
"It is also important that everyone knows what this means for them – this study will help in our fight against the virus, but testing positive for antibodies does not mean you are immune to COVID-19.
"Regardless of the result of an antibody test, everyone must continue to comply with government guidelines including social distancing, self-isolating and getting a test if you have symptoms and always remember Hands, Face, Space."
The findings showed that the number of people with antibodies in England fell by 26.5% between 20 June and 28 September – from 6.0% of the population to 4.4%.
While the number of people testing positive for antibodies declined gradually in the population regardless of employment type, the number of health care workers testing positive for antibodies didn’t change over time.
This may reflect higher initial exposure or boosting from repeated exposure, researchers say.
It remains unclear whether antibodies provide any effective level of immunity or, if such immunity exists, for how long it might last.
Professor Paul Elliott, Director of the REACT programme at Imperial from the School of Public Health, said: " Our study shows that over time there is reduction in the proportion of people testing positive for antibodies against the virus that causes COVID-19.
"It remains unclear what level of immunity antibodies provide, or for how long this immunity lasts.
"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."