Immunity to coronavirus may only last a few months, scientists have warned.
They said a recent study measuring the prevalence of coronavirus antibodies in England showed immunity was ‘waning quite rapidly’, which could lead to an increased risk of reinfection.
Researchers from Imperial College London added it still remains unclear what level of immunity antibodies provide, or for how long this immunity lasts.
Professor Paul Elliott, director of the programme at Imperial, from the school of public health, said: ‘Our study shows that over time there is reduction in the proportion of people testing positive for antibodies against the virus that causes Covid-19.
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‘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.’
The study, called the Real-Time Assessment of Community Transmission (React-2), found a decline in protective antibodies against the disease, with just 4.4% of adults having some kind of immunity against Covid-19 in September.
This is compared with 6% found to have antibodies between June 20 and July 13, and 4.8% between July 31 and August 31.
It comes as cases have started to rise rapidly again in a second peak of the pandemic.
Graham Cooke, professor of infectious diseases at Imperial, said: ‘The big picture here is that after the first wave [of coronavirus], the great majority of the country still did not have evidence of protective immunity.
‘So although we are seeing a decline in the proportion of people who are testing positive, we still have a great majority of people who are unlikely to have been exposed.
‘So the need for a vaccine is still very large if you want to try and get a large level of protection in the population.’
The study, which took place between late June and September, had three rounds of testing and 365,104 adults took part.
Antibody levels reportedly fell by 26.5% overall during the three-month period.
Those aged 18-24 had the highest prevalence of antibodies and lowest decline in antibody levels at 14.9%.
Meanwhile, people aged 75 and over had the lowest prevalence and saw the largest drop, with antibody levels falling by 39%.
The study also found there was no change in antibody positivity in healthcare workers between June and September.
Helen Ward, professor of public health at Imperial College London, said this could indicate ‘ongoing transmission’ of coronavirus in those settings or ‘repeated exposure’.
‘Even at best, (in the first round of the study) 94% of the population remained not likely protected, and now that has declined to over 95% of the population who don’t have evidence of antibodies,’ she said in relation to herd immunity.
‘So I think we are a long, long way from any idea that the population will be protected by other people.’
She added immunity in England was ‘waning quite rapidly’.
In the latest round of the study, between September 15-28, the prevalence of antibodies remained highest in London, and in those of black and Asian ethnicity.
The decline in people testing positive for antibodies was largest in those who did not report having had Covid-19, compared to those who said they had previously tested positive for the virus.
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