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.
Experts at Cambridge University’s MRC Biostatistics Unit estimate 7.37million people have caught the coronavirus already in England, and therefore would likely have immunity.
The PHE study, however, suggests the proportion of people with some level of immunity could be around one in four, which would equate to twice as many people at 14million or more.
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 (stock image)
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.
WHAT ARE T CELLS?
T cells are ones produced by the immune system to help the body destroy invading viruses and to remember how to do so if someone gets infected again.
When the body is invaded by bacteria, a virus or parasites, an immune system alarm goes off, setting off a chain reaction of cellular activity in the immune system.
T lymphocytes (T cells) are white blood cells that are a major part of the immune system.
They are part of the adaptive immune system, which is considered the more specialised response. They use past interactions to remember foreign threats and how to attack them.
The adaptive immune system kicks in after the innate immune system, which is the immediate response to a virus, or ‘first line of defense’.
There are several different types of T cells, some of which are better understood than others:
Killer T cells directly kill the body’s own cells that have already been infected by a foreign invader, while helper T cells stimulate other parts of the immune response – such as B cells.
B cells are also part of the adaptive immune system. They help make antibodies which are specific to each pathogen.
Antibodies are able to block the novel coronavirus by attaching to it and marking it for destruction by other immune cells.
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.
Blood testing surveys by Public Health England suggest that levels of antibody immunity, which is different to T-cell immunity, are lower than 10 per cent in all regions of England. Graph shows the percentage of people testing positive for antibodies
‘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.’
UP TO 1 IN 10 RECOVERED COVID PATIENTS ‘COULD CATCH IT AGAIN’
People who have already had Covid-19 ‘should not be blasé’ about the virus because up to one in 10 people could catch it again, a top scientist has warned.
Professor Danny Altmann, an immunologist at Imperial College London, said on Monday that the rate of coronavirus reinfection is ‘quite a lot higher’ than data suggests.
His comments came as Prime Minister Boris Johnson went into a fortnight of self-isolation after coming into close contact with an MP who later tested positive.
Professor Danny Altmann
The PM claimed he is ‘bursting with antibodies’ after ending up in intensive care during his own severe bout of Covid-19 in the country’s first wave.
Professor Altmann, however, said although the risk of catching the disease again is ‘low’, it could happen to as many as one in 10 people and recovered patients should still take it very seriously.
Scientists have reported a handful of cases of coronavirus reinfection — but the circumstances around them are often hazy. Most scientists investigating the topic agree that it’s unlikely survivors will be struck down again within a year.
The Imperial expert said there had been around 25 ‘hard confirmed cases’ in the world of people catching Covid-19 twice, but that researchers think it is far more common.
And those who do get reinfected are likely to be protected from a severe bout of the disease, experts say. But whether it is more or less serious, Professor Altmann said, is still a topic for debate.
‘I read a lot about people saying one can’t be reinfected or there’s practically zero risk of reinfection,’ he said on BBC Radio 4’s Today programme.
‘That’s not quite true because, of 50million plus cases of infection in the world, we have more than 25 hard confirmed cases of reinfection, which you might say is negligible, but that’s because academically we set the bar quite high for defining reinfection.
‘You have to be SARS positive and then negative and then positive again and [with] different virus sequences and things.
‘Anecdotally, I think most of us think the rate of reinfection is quite a lot higher than that but not enormous.’