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Defining correlates of protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine breakthrough infection informs vaccine policy for booster doses and future vaccine designs. Existing studies demonstrate humoral correlates of protection, but the role of T cells in protection is still unclear. In this study, we explore antibody and T cell immune responses associated with protection against Delta variant vaccine breakthrough infection in a well-characterized cohort of UK Healthcare Workers (HCWs). We demonstrate evidence to support a role for CD4+ and CD8+ T cells as well as antibodies against Delta vaccine breakthrough infection. In addition, our results suggest a potential role for cross-reactive T cells in vaccine breakthrough.

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COVID vaccine, COVID-19, Delta, SARS-CoV-2, T cells, antibody, immunity, vaccine breakthrough, Humans, Case-Control Studies, Breakthrough Infections, Antibodies, CD8-Positive T-Lymphocytes, SARS-CoV-2, Vaccines, CD4-Positive T-Lymphocytes, Antibodies, Viral, Antibodies, Neutralizing