Covid-19: Powerful T cells likely to protect against severe illness from Omicron, SA and US studies find

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  • Omicron is capable of evading antibodies and causing reinfection and breakthrough infections.
  • But it barely evades T cells, shows two new studies, which support the epidemiological data experts have been observing.
  • This means vaccinated and recovered people are likely to retain good protection against severe disease caused by Omicron.

Most of the disease-fighting T cells acquired through vaccination and prior Covid-19 infection still recognise the Omicron variant and should offer protection against serious illness, a new South African study has found.

Omicron is known to evade antibodies, one arm of the immune system and the first line of defence against infection. But, as the latest data shows, it is unable to evade T cells, which protect against severe disease.

The study, posted to medRxiv on Wednesday and which has been submitted for peer review, was carried out by researchers at the University of Cape Town's (UCT) Institute of Infectious Disease and Molecular Medicine.

The findings may explain why, despite the rapid rise in cases, the country has been reporting fewer hospitalisations during its fourth wave. According to seroprevalence studies, more than 70% of South Africans have already contracted Covid-19, while around 45% of the population have been vaccinated.

The findings were "good news", co-author Professor Wendy Burgers, a viral immunologist at the Division of Medical Virology at UCT, wrote on Twitter.

She said:

Despite Omicron having so many mutations, and lower antibody activity, the majority of T cell responses, from vaccination or infection, cross-recognise the new variant.

T cells maintained

In test tube experiments, the scientists tested the extent to which the new variant of concern could neutralise the "cellular response" to the Covid-19 virus.

Participants with prior infection, as well as those who had received the Pfizer-BioNTech or Johnson & Johnson vaccines, were included in the study.

"We found that 70 to 80% of the CD4 and CD8 T cell response to [Omicron's] spike was maintained across study groups," the authors wrote.

"The limited effect of Omicron's mutations on the T cell response suggests that vaccination or prior infection may still provide substantial protection from severe disease," they added.

"Indeed, South Africa has reported a lower risk of hospitalisation and severe disease compared to the previous Delta wave."

Likely to protect against future variants

These T cell responses, which are the body's second line of defence, may also protect against future variants. 

"The resilience of the T cell response demonstrated here also bodes well in the event that more highly mutated variants emerge in the future," the authors said.

"Well-preserved T-cell immunity to Omicron is consistent with early clinical observations from South Africa, UK and Scotland of lower severity – a decoupling of caseloads from hospitalisations, and shorter hospital stays, which may be due to this remaining T cell immunity," Burgers wrote in a Twitter thread.

US study shows similar results

A US study, posted shortly after the SA study, demonstrated similar findings.

"Our data demonstrate that the vast majority of T cell epitopes are fully conserved… suggesting that the continued evolution of variants has not been associated with increased escape from T cell responses at the population level," wrote researchers at the La Jolla Institute for Immunology in southern California, whose paper appears in preprint server bioRxiv.

"This data provides reason for optimism, as most vaccine-elicited T cell responses remain capable of recognising all known SARS-CoV-2 variants," they added.

*For more Covid-19 research, science and news, click here. You can also sign up for our Daily Dose newsletter here.

READ | Covid-19: More than 90% of hospital deaths in 4th wave are in unvaccinated, partially vaccinated people

READ | Rates of Covid-19 hospitalisation lower in fourth wave - NICD

READ | Withdrawal of new Covid-19 guidelines 'extremely disappointing', says Rural Doctors Association

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