A quarter of front-line workers may already be immune to coronavirus, a new study has found.
The study of nearly 3,000 key workers from the police, fire and health services was designed to discover levels of immunity to the virus.
It was discovered that by June, one in four had high levels of T-cells which recognised coronavirus which suggests some level of protection against the virus despite nearly half having never been infected.
T-Cells are a type of white bloody cell which makes up part of a healthy immune system. They are thought to be essential to protect against infection from Covid-19 and could provide longer term immunity than antibodies.
The study by Oxford Immunotec and Public Health England found that no participants with a high T-cell response developed symptomatic coronavirus infection when researchers followed up with them.
Until now most research has been focused on antibodies. Antibodies work differently to T-Cells and aim to neutralise a virus before it enters the body's cells whereas T-cells target and destroy cells that are already infected by the virus.
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Dr Peter Wrighton-Smith, the CEO of Oxford Immunotec, the company that developed the T-cell test for trial, told the Telegraph that the study shows antibody testing alone may underestimate the number of people already immune to the virus.
He said: "Here we are talking about people on the front line, 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."
"It also suggests that models predicting the outcome of the pandemic are unduly thinking more people are going to get it than really are.
"In this data, there is a significant cohort of people who have T-cells without antibodies. Clearly some of this may be because those antibodies have waned over time, but some is probably immunity from other infections.
"There has been growing speculation that there is a phenomenon of cross-reactive immunity in which people who have been exposed to a common cold virus will also be protected from Covid."
The study was a pre-print and has not been published in a journal or peer reviewed.
