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Levels of protective antibodies against COVID-19 wane after infection, researchers say.
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Antibodies that may protect against COVID-19 in people who have previously had the virus declined over the summer, according to a new study that could throw doubt on the idea that a population can develop herd immunity.
The React-2 study, published on Tuesday, found the number of people testing positive for antibodies has fallen by 26% between June and September — from almost 6% of all participants to just 4.4%.
The study by Imperial College London was released as a preprint paper, which means the research hasn’t yet been peer-reviewed.
The researchers screened more than 365,000 adults in England who had taken three antibody tests between June and September. Antibodies, a key part of immune defenses, can help stop the virus from getting inside the body’s cells.
Those aged 18-24 had the highest prevalence of antibodies and lowest decline in antibody levels at 14.9%. People aged 75 and over had the lowest prevalence and saw the largest drop, with antibody levels falling by 39%.
“Nevertheless, the data do lend weight to the concern that antibodies induced by natural infection may be short-lived (as is the case for other seasonal coronaviruses)” said Eleanor Riley, professor of immunology and infectious disease at the University of Edinburgh, who wasn’t involved in the research.
Professor Paul Elliott, director of the program at Imperial College, said the study shows that over time there is a reduction in the proportion of people testing positive for antibodies.
However, he warned that testing positive for antibodies doesn’t mean people are immune to 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,” Elliott said.
The findings suggest that immunity to COVID-19 may wane over time, calling into question the idea of herd immunity, whereby at least 50% of a community can develop immunity to a virus and reduce person-to-person transmission.
So far in the pandemic there has been mixed research about the longevity and effectiveness of COVID-19 antibodies.
Read: Doctors and scientists take aim at herd immunity, calling it ‘nonsense’ and a ‘nebulous’ idea
On Oct. 15, the government’s science advisory group Sage warned that herd immunity isn’t possible and trying to implement the strategy would lead to a new wave of coronavirus cases.
Sage said that it wouldn’t be possible to prevent the virus spreading from younger people to older people, and that “a very large proportion of the population would need to withdraw from daily life for many months, which would have profound negative effect on them.”
The University of Edinburgh’s Riley said the study suggests that antibodies that can be detected by a simple do-it-yourself test may not persist beyond about three months after infection. “If true, then these tests are unlikely to be useful for estimating cumulative population exposure to the virus or for individuals to use to assess their own previous exposure.”
Riley said that the study doesn’t look at antibody concentrations, antibody function, or other aspects of immunity such as T cell immunity (which is a metric that investors are tracking in COVID-19 vaccine developments), and it doesn’t look at the trajectory of antibody levels in the same individuals over time.
Read: There are four coronavirus vaccines in late-stage studies — here’s how they differ
The React-2 study comes as weekly deaths linked to coronavirus have risen in England and Wales for the sixth week in a row, according to data released on Tuesday by the Office for National Statistics.
The Imperial College researchers said their findings don’t dash hopes of a vaccine.
“The big picture is after the first wave, the great majority of the country didn’t have evidence of protective immunity, said Professor Graham Cooke, one of the researchers, adding: “The need for a vaccine is still very large, the data doesn’t change that.”
On Oct 12., a University of Arizona Health Sciences Study that examined a sample of nearly 6,000 COVID-19 patients, showed that antibodies persist for months after infection, providing long-term immunity.
“We clearly see high-quality antibodies still being produced five to seven months after SARS-CoV-2 infection,” said Deepta Bhattacharya, associate professor of immunobiology, at University of Arizona College of Medicine.
Jonathan Ball, professor of molecular virology at the University of Nottingham, said that while the React-2 study confirms suspicions that antibody responses — especially in vulnerable, elderly populations — decrease over time, it was less clear what the relationship between waning immunity and susceptibility to reinfection and the resulting severity of any subsequent infection was.
“Antibodies are likely to be important in protecting us from future infection and disease, but other arms of the immune system, for example cellular immunity, might also be key. Therefore, it is essential that we gain a better understanding of what protective immunity looks like and this can only be gleaned by measuring all aspects of immunity following infection and seeing how this relates to reinfection risk,” Ball said.
Read: COVID-19 reinfection documented in Nevada man
There are several documented cases of reinfection in the U.S. and abroad, including a 25-year-old man in Reno, Nevada, who was infected with two separate strains of the virus within a two-month period.
Other research published in September in the New England Journal of Medicine indicated that antibodies decay in some people who have had mild cases of COVID-19 within three months.
