Two types of white blood cells play a key part in our immune systems: B cells and T cells. T cells can both attack infected cells and help B cells produce antibodies.
T cells cannot prevent infections, because they only kick in after a virus is in the body, but they do help clear an infection, which could make a difference to overall illness, reports the science journal Nature.
They may also reduce transmission by restricting the amount of virus circulating in an infected person.
Cells that are infected display viral proteins on their surface, which T cells can recognise and then destroy infected cells.
Crucially, antibodies can only target proteins on the outside of a virus, while T cells can learn to recognise any viral proteins.
However, most vaccines focus on prompting antibodies against the viral ‘spike’ which penetrates cells, because antibodies bind to the viral proteins and block infection.
This gives excellent levels of protection against extreme illness, but antibodies wane over time and this ‘spike’ region of viruses can mutate.
While more research needs to be done to fully understand the relationship between T cells and Covid immunity, early findings suggest that they could help provide a longer lasting protection against the disease.
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According to one recent study, a proportion of people experience “abortive infections”, where T cells destroy the virus very soon after it enters the body, because they have T cells likely gained from exposure to other similar viruses.
The New Scientist reports the University College London study found that around fifteen percent of healthcare workers in a cohort tracked during the first wave experienced this, despite not having antibodies.
The scientists behind the study suggested that because T cells can target the internal replication machine of a virus, a vaccine which produces a strong T cell response could also protect against a broader range of variants and coronaviruses.
Most vaccines work by priming antibody responses, but many also have an effect on T cell responses.
However, researchers have yet to establish how effective a vaccine which only produces T cells would be.
On Tuesday, the head of AstraZeneca, Pascal Soriot, suggested that the Oxford vaccine’s promotion of T cells in elderly recipients could mean more durable immunity, and explain why countries which did not use it are experiencing high levels of infections.
“What I’m saying is that T-cells do matter and in particular it relates to the durability of the response, especially in older people, and this vaccine has been shown to stimulate T-cells to a higher degree in older people,” he said.
However Professor Danny Altmann, of Imperial College London, said it would be very difficult to pinpoint the choice of vaccine as the key factor behind the differences in countries’ infection rates.
“It would be slightly foolhardy to try and attribute that to the quite nuanced differences in choices of vaccine across different countries,” he told the Guardian.
“I don’t know where you’d start to do that scientifically.”
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