Cellular and humoral immune response to a third dose of BNT162b2 COVID-19 vaccine – a prospective observational study

Background Since the introduction of various vaccines against SARS-CoV-2 at the end of 2020, rates of infection have continued to climb worldwide. This led to the establishment of a third dose vaccination in several countries, known as a booster. To date, there has been little real-world data about the immunological effect of this strategy. Methods We compared the humoral- and cellular immune response before and after the third dose of BioNTech/Pfizer vaccine BNT162b2, following different prime-boost regimes. Humoral immunity was assessed by determining anti-SARS-CoV-2 binding antibodies using a standardized quantitative assay. In addition, neutralizing antibodies were measured using a commercial surrogate ELISA-assay. Interferon-gamma release was measured after stimulating blood-cells with SARS-CoV-2 specific peptides using a commercial assay to evaluate the cellular immune response. Results The median antibody level increased significantly after the third dose to 2663.1 BAU/ml vs. 101.4 BAU/ml (p < 0.001) before administration of the boosting dose. This was also detected for neutralizing antibodies with a binding inhibition of 99.68% ± 0.36% vs. 69.06% ± 19.88% after the second dose (p < 0.001). 96.3% of the participants showed a detectable T-cell-response after the third dose with a mean interferon-gamma level of 2207.07 mIU/ml ± 1905 mIU/ml. Conclusion This study detected a BMI-dependent increase after the third dose of BNT162b2 following different vaccination protocols, whereas all participants showed a significant increase of their immune response. This, in combination with the limited post-vaccination-symptoms underlines the potential beneficial effect of a BNT162b2-boosting dose.