Brush with a cold ‘boosts Covid immunity’

Many who have never been infected could be protected against virus after exposure to similar coronaviruses

A QUARTER of people may already be immune to coronavirus even though many have never been infected, a study by Public Health England suggests.

Over the past few months, researchers have been following nearly 2,850 key workers from the police, fire and health services to gauge levels of immunity to the virus.

They discovered that by June, one in four had high levels of T-cells which recognised Covid, suggesting they had some level of protection against the virus – even though nearly half had never been infected with coronavirus.

Researchers believe that they probably picked up immunity from other similar coronaviruses, such as those which cause the common cold. In the four months of follow up, nobody with a high T-cell count became infected with

Covid-19, suggesting they are protected against the virus.

Dr Peter Wrighton-smith, chief executive of Oxford Immunotec, the firm that developed the T-cell test for trial, said it showed that antibody testing alone may underestimate the number of people who are immune to the disease.

“Here we are talking about people on the frontline, so 25 per cent may be a bit high, but this suggests we are not seeing a true picture through antibody surveillance surveys, and that many more people have T-cell immunity,” he said.

“It also suggests that models predicting the outcome of the pandemic are unduly thinking more people are going to get it than really are.

“There has been growing speculation that there is a phenomenon of crossreactive immunity in which people who have been exposed to a common cold virus will also be protected from Covid.”

At least six studies have now reported T-cell activity against coronavirus in 20 to 50 per cent of people with no known exposure to the virus.

In blood donor samples taken in the US between 2015 and 2018, around half showed some kind of immune resistance to Covid – even though they were taken years before the disease emerged.

Likewise in the Netherlands, coronavirus-fighting T-cells were found in two of 10 people who had not been exposed to the virus.

Currently, the MRC Biostatistics Unit Covid-19 Working Group at Cambridge University estimates that around 7.4 million people in England have had coronavirus. But the study suggests the true number of people who are immune could be closer to 14 million.

The study also found that among those who had never had coronavirus, under-30s were more likely to have high levels of T-cells compared to over60s, which could explain why young people are at less risk from the virus.

The study is the first to show T-cells offer protection against coronavirus.

Dr David Wyllie, lead author of the study, said: “Four months into the study, 20 participants with lower T cell responses had developed Covid-19, compared with none among individuals with higher T cell responses.

“This suggests i ndividuals with higher numbers of T-cells may have some level of protection from Covid-19.”