Immunology: Vaccination and infection induced T cell responses maintained against Omicron

The majority of T cell responses against the SARS-CoV-2 spike protein, induced by vaccination or infection, are maintained against Omicron according to a study involving 138 participants published in Nature. However, it is yet to be determined whether the preserved T cell responses contribute to protection from severe COVID-19.

With over 30 mutations in the spike protein of Omicron, it has previously been documented that this variant has the ability to evade a substantial proportion of neutralizing antibody responses. However, the extent to which other components of the immune response, such as T cells, may still target Omicron is unclear.

Catherine Riou, Wendy Burgers and colleagues examined T cell responses in individuals who had previously been vaccinated or infected with earlier variants of SARS-CoV-2 to determine their ability to recognize the spike protein of Omicron should they become infected. The authors examined the T cell response from a total of 40 individuals who had received either one or two doses of the Johnson & Johnson vaccine, 15 who had received two doses of Pfizer–BioNTech and 15 unvaccinated individuals who had recovered from a previous SARS-CoV-2 infection. They found that 70–80% of the CD4+ and CD8+ T cell responses were maintained against the Omicron spike protein across the study groups.

For 19 patients who were hospitalized with Omicron in South Africa, the authors found that these individuals had T cell responses comparable to those seen in patients who were hospitalized in previous waves of the pandemic, in which the ancestral (17 individuals), Beta (16 individuals) and Delta (16 individuals) variants were dominant. The authors conclude that the extensive mutations of Omicron have had a limited effect on T cell responses to the variant, suggesting that the majority of SARS-CoV-2 spike-specific T cell responses are directed towards conserved regions of this protein.