COVID-19 Immunity in the Cohort of IRCCS San Raffaele Hospital Employees after BNT162b2 Vaccination: A Retrospective Observational Study.

The COVID-19 pandemic represents the most severe health and socioeconomic crisis of our century. It began with the first reports in China, in the Wuhan region in December 2019, and quickly spread worldwide, causing a new Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Among the population most at risk of infection and developing severe forms of the disease are the elderly and healthcare workers, who are more exposed to infected individuals. On December 11, 2020, the Food and Drug Administration approved the emergency use of the BNT162b2 vaccine, the first mRNA vaccine in history. Since then, the total number of vaccine doses administered has exceeded 12 billion. Italy was the first European country to be affected by the pandemic, recording the highest number of total COVID-19 cases (25,695,311) and, after the first 70 days, had the highest crude mortality rate (141.0 per 100,000). In this study, we analyze the rate of SARS-CoV-2 infection among healthcare workers at the San Raffaele Scientific Institute in Milan before and after receiving the BNT162b2 vaccine.