New science explains South Africa's low rates of omicron severe disease

SARS-CoV-2 spike T cell responses induced upon vaccination or infection remain robust against Omicron

https://www.medrxiv.org/content/10.11...

https://www.medrxiv.org/content/10.11...

Institute of Infectious Disease and Molecular Medicine, University of Cape Town

SARS-CoV-2 Omicron variant has multiple Spike (S) protein mutations

These contribute to escape from the neutralizing antibody responses,
reducing vaccine protection from infection

We assessed the ability of T cells to react with Omicron spike
In participants who were vaccinated with Ad26.CoV2.S (J and J) (n = 20)

or BNT162b2 (Pfizer) (n = 15

or in unvaccinated convalescent COVID-19 patients (n = 15)

SARS-CoV-2-specific T cells play a key role in modulating COVID-19 severity and provide protective immunity

Results

70-80% of the CD4 and CD8 T cell response to spike was maintained across study groups

The magnitude of Omicron cross-reactive T cells was similar to that of the Beta and Delta variants

These results demonstrate that,
despite Omicron’s extensive mutations

and reduced susceptibility to neutralizing antibodies,

the majority of T cell response,

induced by vaccination or natural infection, cross- recognises the variant.

Well-preserved T cell immunity to Omicron,

is likely to contribute to protection from severe COVID-19,

supporting early clinical observations from South Africa.

Further explanation

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.

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

Cross-reactive T cell responses acquired through vaccination or infection may contribute to these apparent milder outcomes for Omicron.

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