Why is Omicron causing less severe disease than previous variants? Expert weighs in

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  • T-cells are part of why Omicron is less severe than other variants.
  • T-cells also contributed to fewer hospitalisations in SA during the fourth wave.
  • Boosters, however, play an essential role in neutralising Omicron.

South African and international studies have shown that Covid-19 caused by the Omicron variant of SARS-CoV-2 is less severe than previous variants of concern. A recent local study shows fewer hospitalisations during the Omicron-driven wave than earlier waves.

What makes Omicron less severe than other variants of concern involves T-cells, says Prof Penny Moore, a researcher at the National Institute For Communicable Diseases (NICD).

Speaking at a recent NICD press conference, Moore discussed the immune response to SARS-CoV-2.

What are T cells?

T cells are part of the immune system that fights off disease. The T cells respond to viral infections and boost the immune function of other cells in the body.

According to the University of Oxford’s Centre for Evidence-Based Medicine, T cells kill cells infected with the virus. “T cells directly recognise viral peptides presented at the surfaces of infected cells, causing apoptosis and preventing the virus from spreading further.” T-cells work together with antibodies to fight infection.

T cells remaining effective

Moore says that T cells are part of why Omicron results in fewer deaths in SA. She explains that because Omicron has the highest number of mutations of all known variants, it can evade neutralising antibody responses, reducing vaccine protection, which is bad news.

“T cells [however] reduce the severity of disease and keep most people out of the hospital,” said Moore.

People who have antibodies from vaccination or previous Covid infection have T cells that maintain their role, despite Omicron’s ability to evade immunity. This caused Omicron to be less severe, leading to fewer pneumonia cases.

Importance of boosters 

Moore added that vaccine boosters do, however, enhance immunity from antibodies and T cells against Omicron.

“If you are infected after vaccination, the vaccine-triggered antibodies are boosted further. Booster vaccines boost neutralising antibody titers to higher levels,” she said.

Moore emphasised that studies have shown that booster shots can neutralise Omicron.

“Boosters still remain the safest way to boost all response,” she said.

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

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