AROUND a third of healthy people without symptoms of coronavirus may have developed a immunity to it, a new study suggests.
The research suggests that immunity levels in those without symptoms may be twice as high as was thought.
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The study was carried out by researchers at the Karolinska Institutet in Sweden, the only European country not to enter lockdown, the Telegraph reports.
The research examined levels of T-cell response to Covid-19 as well as antibodies, which have been the focus of measuring levels of protection against coronavirus but which have proved an unreliable indicator.
T-cells are a type of white blood cell that helps the immune system fight viruses.
The Karolinska researchers found 30 per cent of the healthy blood donors studied were found to have developed “T-cell immunity”.
That was twice the number of cases in which antibodies were detected, the non-peer reviewed study found.
The results indicate public immunity could be as much as twice that identified by antibody tests.
That means areas such as London with high infection rates could be further along the path to herd immunity than was thought, says the Telegraph.
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, added: “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.”
Prof Ljunggren said if the Karolinska study’s findings are replicated London, for instance, might have about 30 percent immunity and New York above 40 percent.
One drawback, however, is that while a blood test for Covid-19 antibodies can produce a result in as little as half an hour, the T-cell tests carried out at Karolinska can take as long as six days to set up.