Asymptomatic coronavirus sufferers appear to lose detectable antibodies earlier than people who have shown symptoms of Covid-19, according to one of the largest studies of its kind in the UK, published on Tuesday.
The findings of Imperial College London and market research firm Ipsos Mori also suggest that antibody loss is slower in 18-24 year olds than in those over 75 years of age.
In total, samples from hundreds of thousands of people across England between mid-June and late September showed that the spread of viral antibodies had fallen by more than a quarter.
The study, commissioned by the British government and published on Tuesday by Imperial, shows that people̵
James Bethel, a junior health minister, called it “a critical study that helps us understand the nature of Covid-19 antibodies over time.”
However, participating scientists warned that many things remain unknown about the long-term response of human antibodies to the virus.
“It remains unclear what level of immunity the antibodies provide or how long that immunity lasts,” said Paul Elliott of the Imperial School of Public Health.
The study included 365,000 randomly selected adults who performed three rounds of finger prick tests for coronavirus antibodies at home between June 20 and September 28.
The results showed that the number of people with antibodies fell by 26.5% over the approximate three-month period.
Scaled to a nationwide level, this means that the proportion of the English population with antibodies has fallen from 6.0% to 4.4%, according to the study.
The decline coincided with the spread of the virus, which was falling dramatically across England – and the rest of the UK – after a month-long national shutdown that eased in the summer.
However, the study found that the number of health workers who tested positive for antibodies did not change over time, potentially reflecting repeated or higher initial exposure to the virus.
“This very large study showed that the proportion of people with detectable antibodies decreases over time,” said Helen Ward, one of the lead authors.
“We still don’t know if this will leave these people at risk of reinfection with the virus that causes Covid-19, but it’s essential that everyone continues to follow the instructions to reduce the risk to themselves and others.”
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