The proportion of people in England with antibodies after Covid-19 infection dropped by more than a quarter over three months, a new study has shown, suggesting people's immune response to SARS-CoV-2 wanes over time.
The participants did three rounds of finger-prick tests at home between June 20 and September 28, according to a news release from the Imperial College London.
Researchers noted that immunity to the novel coronavirus "is complex, and may be assisted by T cells, as well as B cells that can stimulate the quick production of antibodies following re-exposure to the virus", the report said.
"On the balance of evidence I would say, with what we know for other coronaviruses, it would look as if immunity declines away at the same rate as antibodies decline away, and that this is an indication of waning immunity at the population level", Wendy Barclay, head of Imperial College London's Department of Infectious Disease, said, per Reuters.
In England, more than 350,000 people have so far taken an antibody test as part of the REACT-2 study.
In the first round of testing at the end of June and beginning of July, around 60 in 1,000 people had detectable antibodies, compared with 44 in 1,000 in the latest round of testing.
In September, only 44 per 1,000 people were positive.
The evidence follows several studies published earlier this year from China, the United Kingdom and the U.S., which found that people's antibody levels declined sometimes as early as two months after infection.
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There was no change in the levels of antibodies seen in health-care workers, possibly due to repeated exposure to the virus.
The study was released as a pre-print paper, and has not yet been peer-reviewed.
"Testing positive for antibodies does not mean you are immune to COVID-19", says Elliott.
A lead study author stressed the importance of mitigation measures.
Similar findings have been discovered in Germany - which showed the vast majority of people did not have antibodies - even in coronavirus hotspots - and that antibodies might fade in those who do.
Regardless of their antibody status, people are still required to socially distance, get tested if they display symptoms and wear face coverings as and when required.
The finger pricks tested for coronavirus antibodies, and results revealed a drop from almost 6% to 4.4% over a three-month span, which researchers said translates to a 26.5% decline.
One strategy these findings do question, however, is whether herd immunity can be achieved through natural infection.
While every single individual may not be immune, the group as a whole has protection.
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Across three rounds in the REACT study, 17,576 results returned positive, and 30% of people were asymptomatic. In England , more than 350,000 people have so far taken an antibody test as part of the REACT-2 study.
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