Medium-Long Term Immunogenicity of BNT162b2 mRNA COVID-19 Vaccine: A Retrospective Cohort Study

Introduction: To combat the COVID-19 pandemic, a mass vaccination campaign was started in Italy and other European countries on December 27, 2020. The first vaccine available to immunize healthcare workers (HCWs) was the BNT162b2 mRNA COVID-19 vaccine (Comirnaty). While many studies have shown a high antibody response after the second vaccine dose, antibody persistence over the medium-long term has yet to be evaluated. Methods: In this study, the medium-long term persistence of anti-SARS-CoV-2 antibodies was determined in a sample of fully vaccinated HCWs at Bari Policlinico General Hospital, Italy. HCWs who completed the vaccination schedule were screened for anti-SARS-CoV-2 IgG on days 15, 30, 60, 90, and 120 after the second vaccine dose. Findings: At each time point, >99% of the screened HCWs were seroprotected. While the geometric mean titer initially declined over time, by 60 days the titer had stabilized. Older subjects seem to lose IgG faster than younger ones. Interpretations: The immunogenicity conferred by the BNT162b2 mRNA vaccine provides further evidence that it is an essential weapon in efforts to bring the COVID-19 pandemic under control. Accordingly, strict measures should be implemented, ranging from the mandatory vaccination of HCWs to strong incentives aimed at achieving vaccination of the large majority of the general population. Funding: None to declare. Declaration of Interest: The authors declare that they have no competing interests. Ethical Approval: The research protocol was approved by Apulian Epidemiological Observatory .