Almost one in 10 Londoners have Covid-19 antibodies but the number who may have “natural protection” against the virus is declining, a major study revealed today.
This has raised concerns that the coronavirus will become like the common cold and people will be at risk of being re-infected annually – further highlighting the importance of developing a vaccine.
The React 2 study by Imperial College London and Ipsos Mori today reported that the proportion of Londoners having antibodies after developing Covid-19 had fallen from about 13 per cent to about 9.5 per cent since the start of the pandemic.
This is still the highest rate in England. Across the country, the researchers found that the prevalence of antibodies fell from an average of six per cent in June to 4.4 per cent last month, a 26 per cent reduction.
Professor Wendy Barclay, one of the researchers, said: “Seasonal coronaviruses that circulate every winter and cause common colds can re-infect people after six to 12 months. We suspect that the way that the body reacts to infection with this new coronavirus is rather similar to that.
“We don’t yet know what level of antibodies is needed in a person’s blood to protect them from infection or reinfection from [Covid 19] but that level is a crucial thing to begin to understand.”
The latest Imperial research is based on finger-prick blood tests done at home by a random sample of almost 160,000 people.
Antibodies were also more commonly found in the 18-24 and 25-34 age groups and in people of BAME heritage.
The study found that people who had not shown symptoms of the virus at the time of infection were more likely to see a rapid decline in antibody levels.
Of the total of 365,000 people to be tested in the three rounds of the study, 17,000 have been found to have detectable antibodies.
Professor Graham Cooke said: “These data suggest the possibility that decreasing population immunity will lead to an increased risk of reinfection, as detectable antibodies are declining in the population.”
The researchers said the study did not weaken the case for a vaccine, “as a good vaccine may well be better than natural immunity” and was likely to operate in a different way to the body’s own defence mechanism against the virus.
It was also the case that any reinfection tended to be less severe – and that, due to the lack of testing in the first wave, it was hard to prove that a person had been re-infected.
They suggested it may take “six months to a year or two years” for a person’s immunity to Covid-19 to wane entirely.