‘Immunity may be twice as high as believed’
UP TO a third of healthy people without symptoms of Covid-19 may have developed immunity to the virus, international research suggests.
The results indicate public immunity could be as much as twice that identified by antibody tests, meaning infection hotspots such as London could be further along the path to herd immunity than was thought.
Until now, efforts to measure levels of protection against coronavirus have focused on antibodies, which have proved an unreliable measure.
At the start of the pandemic, the Government’s advisers suggested at least 60 per cent of the population would need to be infected in order to achieve herd immunity.
Instead, Britain entered lockdown, on the basis of projections suggesting allowing such levels of disease would leave the NHS overwhelmed. But a new study by Karolinska Institutet in Sweden, the only European country not to enter lockdown, suggests immunity levels in those without symptoms may be twice as high as was thought.
It comes as statistics revealed one in seven children in Leicester has now tested positive for Covid-19, with levels tripling in the last month.
The Daily Telegraph has established prevalence is now at 15 per cent among under-18s in Leicester – roughly three times the rate in England overall.
As well as measuring antibody levels, the Swedish research examined levels of T-cell response. T-cells are a type of white blood cell that helps the immune system fight off viruses.
In total, 30 per cent of the healthy blood donors studied were found to have developed “T-cell immunity” – twice the number of cases in which antibodies were detected.
Sampling in the UK suggests around 7 per cent of people in England have developed antibodies, rising to 17 per cent in London. The new research suggests levels of “T-cell” immunity may be significantly higher.
The new study does not show what level of immunity is given by a T-cell response. But scientists are increasingly excited about the role played by T-cells, as they believe it may explain why some groups – in particular children – appear to be more immune.
Marcus Buggert, an assistant professor at Karolinska Institutet said: “What this means is we are probably underestimating the number of people that have some type of immunity.
“If it means that these individuals are totally protected, or if they’re going to get a milder or asymptomatic disease in the future, it’s hard to say.”
Prof Hans-gustaf Ljunggren, the senior co-author of the study, said: “Our results indicate public immunity to COVID-19 is probably significantly higher than antibody tests have suggested. If this is the case, it is of course very good news from a public health perspective.” He said although the Karolinska study was relatively small and yet to be peer-reviewed, if its findings are replicated, they would apply to any city. London, for instance, might have about 30 per cent immunity and New York above 40 per cent.
Anders Tegnell, Sweden’s state epidemiologist, lost credibility at the end of May, when antibody tests found just 7.3 per cent of Stockholm’s inhabitants had developed Covid-19 antibodies by the end of April. This was far short of the 25 per cent he had been estimating.
But Prof Ljunggren said the antibody figures in the Swedish capital had now risen and while researchers had been very puzzled with the low antibody responses, “now when we see significant T cell responses in terms of percentages of people being affected them, it makes sense”.
Meanwhile, a German study has suggested that exposure to the common cold could provide some level of immunity to Covid.