(CNN)A study of hundreds of thousands of people across England suggests immunity to the coronavirus is gradually wearing off – at least according to one measure.

Older patients, women and those with variety of early symptoms most at risk of ‘long Covid,’ paper suggestsResearchers who sent out home finger-prick tests to more than 365,000 randomly selected people in England found a more than 26% decline in Covid-19 antibodies over just three months.”We observe a significant decline in the proportion of the population with detectable antibodies over three rounds of national surveillance, using a self-administered lateral flow test, 12, 18 and 24 weeks after the first peak of infections in England,” the team wrote in a pre-print version of their report, released before peer review.”This is consistent with evidence that immunity to seasonal coronaviruses declines over 6 to 12 months after infection and emerging data on SARS-CoV-2 that also detected a decrease over time in antibody levels in individuals followed in longitudinal studies,”

The US had more daily Covid-19 cases in the past week than ever before. And no, it’s not just due to more testingThe study was published Monday by Imperial College London and Ipsos MORI, a market research company. At the beginning of the study, in June, 6% of those who took the tests had IgG antibody responses to the coronavirus, they reported. By September, just 4.4% of them did. For health care workers, the rates stayed about the same.Antibodies are the proteins your body naturally generates to fight infection. IgG are one type – the tests were not designed to detect other types of antibodies. Other research teams have found that other types of antibodies may persist longer than IgG does.