Covid: What is T cell protection and why does it matter in the fight against Omicron?

·3-min read
A dose of a coronavirus vaccine is prepared (PA) (PA Archive)
A dose of a coronavirus vaccine is prepared (PA) (PA Archive)

As scientists try to understand the new Omicron variant, some vaccine makers say their jabs could provide protection even if the variant partially evades antibody defences.

Dr Ugur Sahin, the scientist behind the Pfizer jab, urged calm over the new ‘super strain’, as he believed there would be substantial protection against severe illness through T cells.

“If a virus achieves immune escape, it achieves it against antibodies, but there is the second level of immune response that protects from severe disease — the T cells,” he said on Tuesday.

The head of AstraZeneca, Pascal Soriot, has previously suggested that the Oxford vaccine’s promotion of T cells in elderly recipients could mean more durable immunity.

His comments came before the discovery of the new Omicron variant.

Researchers are now working to fully understand how effective jabs will be against the mutant strain.

What are T cells and why do they matter?

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.

New figures suggest that around nine in 10 adults in all parts of the UK continue to have Covid-19 antibodies (Joe Giddens/PA) (PA Wire)
New figures suggest that around nine in 10 adults in all parts of the UK continue to have Covid-19 antibodies (Joe Giddens/PA) (PA Wire)

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.

Longer lasting protection?

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.

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 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.

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