Antibody Titers 3-Months Post-Vaccination with the Pfizer/Biontech Vaccine in Greece

Background: The immunization of healthcare workers plays a recognized key role in prevention in the COVID-19 pandemic: in Greece, the vaccination campaign began as soon as early January 2021. The measurement of antibody titers at specific intervals after vaccination leads to tentative conclusions regarding the duration of immunity. Methods: We performed a study on 281 healthcare workers at a tertiary hospital in Greece, vaccinated in January 2021 with two doses of the BNT162b2 vaccine three weeks apart. 38 of them had been infected and recuperated from COVID-19 infection before the first vaccine dose. Three months after the second dose, titers of total RBD-specific IgGs against SARS-CoV-2 and total neutralizing antibodies targeting the viral S1/RBD domain were determined. The trial is registered on the International Standard Randomized Controlled Trial Number registry (study ID: ISRCTN61884303). Results: For 99.64% of the antibody titers were above the threshold of 50 AU/ml a trimester after the two-dose vaccination. Statistically significant differences between age groups were observed (p=0.005). A statistically significant difference was also observed three months after the second dose between subjects with a prior Covid-19 infection relative to those without prior infection (p 90% (59.29% of the subjects) compared to those with<90% (40.71% of the subjects) with corresponding (p<0.001). Conclusion: To our knowledge, this is the first study in Greece investigating the efficacy of the BNT162b2 vaccine, after a full course of a two-dose administration, in inciting creation of neutralizing antibodies in vaccinees and studying the serology after a trimester.