A number of frontline medics at high risk of contracting Covid were able to evade infection possibly because they had previously had a cold caused by a different form of coronavirus, extraordinary research suggested on Wednesday.
The study investigated 58 London hospital staff who never tested positive for Covid despite being at high risk of exposure to the virus in the first wave of the pandemic.
They had higher levels of T cells — the body’s immune memory cells — suggesting that these had attacked cells that had been infected with Covid and rapidly halted the spread of the virus.
UCL’s Dr Leo Swadling said: “Previous common cold exposure may have given these individuals a head start against the virus, tipping the balance in favour of their immune system eliminating the virus before it could start to replicate.”
The study, published in Nature, is the latest groundbreaking piece of research from the COVIDsortium research programme that was set up early in the pandemic by staff at St Bartholomew’s hospital.
However the researchers, speaking at a briefing at the Science Media Centre, made clear that not all colds would protect against current covid infections.
This is because only about 10 per cent of common colds are caused by a coronavirus. In addition, the study only looked at the impact of the original Wuhan strain of Covid-19, not the more infectious Delta strain that has been dominant in the UK for months.
The published research suggests that by designing vaccines able to activate T cells, it may be possible to halt Covid far earlier if the “replication proteins” in its internal system can be disabled.
This would be a different approach from that taken by currently available vaccines, which target the spike protein that protrudes from the Covid virus.
It would open the door to a vaccine effective against Covid-19, coronaviruses that cause colds and new animal coronaviruses, and offer an “additional layer of protection” to the current jabs.
Professor Mala Maini, the senior study author, said: “A vaccine that can induce T cells to recognise and target infected cells expressing these proteins... would be more effective at eliminating early SARS-CoV-2, and may have the added benefit that they also recognise other coronaviruses that currently infect humans or that could in the future.
“This dual-action vaccine would provide more flexibility against mutations, and because T cells can be incredibly long-lived could also provide longer-lasting immunity.”
Dr Andrew Freedman, reader in infectious diseases at Cardiff University School of Medicine, said: “This is an important study which may help to explain why some people who were repeatedly exposed to Covid-19 before the vaccine rollout apparently did not catch it.
“It appears that some of them had pre-existing memory T cell immunity to a protein involved in replication of the virus, probably induced by previous infection with other seasonal coronaviruses.
“The immune system was able to clear the virus rapidly before it could cause symptoms or be detected either by PCR or antibody production.
“As the authors point out, this finding could lead to the development of novel vaccines which might confer long lasting protection against SARS-CoV-2 and other coronaviruses, including ones that might emerge and pose a threat in the future.”
Dr Alexander Edwards, associate professor in biomedical technology, University of Reading, said: “T cells, white blood cells that play a central role in out immune system, can ‘sniff out’ coronavirus proteins even when buried within the virus particle, in contrast to antibodies that ‘grab hold’ of shapes on the surface.
“This excellent and thorough study identifies a group of people who are likely to have been exposed to the Covid-19 virus but didn’t appear outwardly to have experienced an infection.
“This provides hard evidence for what might be expected from virus-host biology – different people can expect different outcomes after being exposed to a virus. Sometimes you may be lucky and not get infected; other times you might be fully infected and experience mild or severe disease.
“Insights from this study could be critical in design of a different type of vaccine. A vaccine that primes T cell immunity against different viral protein targets that are shared between many different coronaviruses would complement our spike vaccines that induce neutralising antibodies.
“Hopefully this study will lead to further advances in vaccine development, as we need all the types of vaccine we can get.”