BNT162b2 mRNA SARS-CoV-2 Vaccine Elicits High Avidity and Neutralizing Antibodies in Healthcare Workers

The BNT162b2 vaccine, containing lipid nanoparticles-formulated mRNA encoding the full-length spike protein of SARS-CoV-2, has been employed to immunize health care workers in Italy, administered in two doses 21 days apart. In this study, we characterized the antibody response induced by the BNT162b2 vaccine in a group of health care workers, tested at baseline, after the first dose and after the booster. Thirty-nine subjects without previous exposure to SARS-CoV-2 were vaccinated with the BNT162b2 vaccine. IgM, IgG, and IgA anti-receptor binding domain (RBD) were tested by ELISA. Neutralizing antibodies were evaluated testing the inhibition of RBD binding to ACE2. Antibody avidity was measured by urea avidity ELISA. IgM anti-RBD are produced after the first dose of vaccine and persist after the booster. IgG and IgA anti-RBD antibodies are detected in high amounts in all the subjects after the first dose and further increase after the booster. A few subjects, already after the first dose, produce antibodies inhibiting RBD interaction with ACE2. After the booster, high levels of inhibitory antibodies are detected in all the subjects. Affinity maturation takes place with boosting and IgG anti-RBD avidity increases with the number of immunizations. A less pronounced increase is observed with IgA. These data indicate that the BNT162b2 vaccine can induce high levels of protective antibodies of high avidity in vaccinated subjects; both IgG and IgA anti-RBD antibodies are produced. Further studies are needed to evaluate antibody persistence over time.