Vaccines elicit highly conserved cellular immunity to SARS-CoV-2 Omicron

The highly mutated SARS-CoV-2 Omicron (B.1.1.529) variant has been shown to evade a substantial fraction of neutralizing antibody responses elicited by current vaccines that encode the WA1/2020 spike protein¹. Cellular immune responses, particularly CD8⁺ T cell responses, probably contribute to protection against severe SARS-CoV-2 infection^2-6. Here we show that cellular immunity induced by current vaccines against SARS-CoV-2 is highly conserved to the SARS-CoV-2 Omicron spike protein. Individuals who received the Ad26.COV2.S or BNT162b2 vaccines demonstrated durable spike-specific CD8⁺ and CD4⁺ T cell responses, which showed extensive cross-reactivity against both the Delta and the Omicron variants, including in central and effector memory cellular subpopulations. Median Omicron spike-specific CD8⁺ T cell responses were 82-84% of the WA1/2020 spike-specific CD8⁺ T cell responses. These data provide immunological context for the observation that current vaccines still show robust protection against severe disease with the SARS-CoV-2 Omicron variant despite the substantially reduced neutralizing antibody responses^7,8.