Lower probability and shorter duration of infections after COVID-19 vaccine correlate with anti-SARS-CoV-2 circulating IgGs
Chiara Ronchini, Sara Gandini, Sebastiano Pasqualato, Luca Mazzarella, Federica Facciotti, Marina Mapelli, IEO Covid Team, Gianmaria Frigè, Rita Passerini, Luca Pase, Silvio Capizzi, Fabrizio Mastrilli, Roberto Orecchia, Gioacchino Natoli, Pier Giuseppe Pelicci
Abstract
The correlation between immune responses and protection from SARS-CoV-2 infections and its duration remains unclear. We performed a sanitary surveillance at the European Institute of Oncology (IEO) in Milan over a 17 months period. Pre-vaccination, in 1,493 participants, we scored 266 infections (17.8%) and 8 possible reinfections (3%). Post-vaccination, we identified 30 infections in 2,029 vaccinated individuals (1.5%). We report that the probability of infection post-vaccination is i) significantly lower compared to natural infection, ii) associated with a significantly shorter median duration of infection than that of first infection and reinfection, iii) anticorrelated with circulating antibody levels.