Natural coronavirus immunity could be TWICE as common as experts thought, PHE says

Natural immunity to the coronavirus could be twice as common as experts believed, according to a Public Health England study.  

Researchers at PHE found T-cells – a key part of the immune system – in a far higher number of people than expected.

The cells are vital for destroying human cells that have been infected with coronavirus to stop them going on to infect others – antibodies and other parts of the immune system can’t get to the virus once it gets this far in.

The research, among 2,847 key workers from the NHS, police and fire service in June, found that 25 per cent of participants had high levels of T-cells which recognised Covid. 

That is far higher than the results of antibody surveys, which have consistently found no more than six per cent test positive for having had Covid. And it is likely to be even higher now that the country has experienced a second wave of infections.

While experts at Cambridge University’s MRC Biostatistics Unit estimate 7.37million people have caught the coronavirus already, and therefore would have immunity, the PHE study suggests the true number of people with some level of immunity could be 14million or more.

Until now much of scientists’ attention has been focused on antibodies, which neutralise a virus before it enters the body’s cells. 

T-cells, in comparison, target and destroy cells that are already infected by the virus.

Crucially, the researchers found that none of those with high T-cell responses became infected with Covid in the following four months – suggesting this part of the immune system is an effective protective factor. 

They also found that only half of those who had high T-cell responses had any identifiable Covid antibodies, suggesting some immunity may exist without antibodies.

Dr Peter Wrighton-Smith, of Oxford Immunotec, the company that developed the T-cell test, said: ‘The implication is that there is a population of people who are protected from Covid who are not being picked up by the antibody studies.’ 

He stressed that the people in the study were all frontline workers so were more likely to have been exposed to Covid.

The researchers believe this could suggest two possibilities. One theory is that antibodies fade very quickly after someone recovers from Covid – but T-cells are longer lasting.

Another is that people are left with immunity after suffering from similar coronaviruses – such as those which cause the common cold – even if they have never been infected with Covid itself.

But Dr Wrighton-Smith added: ‘We are not picking up all cases with the antibody surveys – so more people may be protected than we thought.’ 

Dr David Wyllie, a consultant microbiologist at Public Health England and the 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 individuals with higher numbers of T-cells recognising SARS-CoV-2 may have some level of protection from Covid-19, although more research is required to confirm this.’

Professor Karol Sikora, a cancer expert at the University of Buckingham, was one of the first to raise the importance of T-cells early on in the pandemic.

In a video posted on Twitter last night he said: ‘This is really good news. This means almost certainly the T-cell response is innate – it is [triggered] by something people have been exposed to in the past.

‘So when Corona comes along they are not susceptible.

‘It suggests more people have protection than antibody surveys estimate, but also many probably have residual immunity to Covid-19 from other infections.

‘T-cells have been overlooked for too long. This proves that has to change.’

But Dr Rupert Beale of the Francis Crick Institute in London, said the issue may be to do with the antibody tests used.

‘About a quarter had highly reactive T cells, more than half of them had serological evidence of prior infection using tests that would be about 70 per cent sensitive – so only a very small proportion of adults (less than 10 per cent, maybe much less than 10 per cent) would be protected by pre-existing T cell immunity.’