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The proportion of people in England with antibodies to the coronavirus fell by more than a quarter in the space of three months, the researchers have revealed, fueling concerns about reinfection.
The findings come from the React-2 study, which is based on the results of home fingerstick antibody tests of randomized participants from 314 local authorities.
The first results, based on data from 100,000 people, were published in August and revealed that around 6% of England’s population had the antibodies, protective proteins produced in response to an infection, although the team says it could be a slight understatement.
The new work, which has not yet been peer-reviewed, extends this with more tests in two new cohorts, each of which returned results from more than 100,000 adults.
The results reveal that only 4.4% of those tested in the most recent round, between September 15 and 28, had detectable coronavirus antibodies.
“Taken together, these data suggest the possibility that declining immunity in the population leads to an increased risk of reinfection as detectable antibodies decrease in the population,” said Graham Cooke, co-author of the report and professor of infectious diseases. at Imperial College, London. .
The researchers said that antibodies would be expected to decline over time, but how long it takes and how much levels fall differs between viruses, factors that are important when it comes to how long protection lasts.
Professor Wendy Barclay, chair of influenza virology at Imperial College London and a co-author of the report, said it was not yet known what level of antibodies is needed to protect someone from infection or reinfection with Covid-19, but Experiments suggested that it might be approximately the same level as the detection threshold of the antibody test.
Some have raised the possibility that other components of the immune system may continue to offer protection even if antibodies have declined, such as T cells, which can kill infected cells, or memory B cells, which can rapidly produce new antibodies. However, the team said it is too early to know if that is the case, or how long that protection might last, while it is difficult to measure the levels of such T cells.
“The fact that people are regularly reinfected throughout their lives with seasonal coronaviruses [that cause common colds] suggests that immunity, whether or not antibody-mediated and / or T-cell mediated, is probably not very durable, ”Barclay said, adding that the team suspects that the body reacts to infection with the new coronavirus in a similar way. .
But he said the new results don’t necessarily mean that immunity from vaccination is short-lived. “A good vaccine can be better than natural immunity.”
Barclay added that if a second infection did occur, immune memory could mean it would be less severe than the first. But, he noted, data is currently lacking – only a few cases of reinfection have been confirmed worldwide so far.
The team said antibodies remain a good indicator of protection against reinfections, adding that the low prevalence of coronavirus antibodies and the rapid rate at which they have been shown to fall undermine the case for a herd immunity policy without a vaccine.
“When you think that 95 out of 100 people are unlikely to be immune, and therefore likely to be susceptible, then we are very, very far from anything that looks like population-level protection against transmission. progressive, “said co-author Helen Ward, professor of public health at Imperial.
The team said the lack of reinfections could be because such cases are difficult to confirm, but it may also be that not enough time has passed for antibody levels to drop to the point where most people are susceptible to. reinfection.
Cooke added that it remains important for the public to adhere to Covid restrictions, while a vaccine is also needed. “The big picture here is that after the first wave, the vast majority of the country still had no evidence of protective immunity,” he said.
