ABSTRACT
The management of future booster COVID-19 vaccination requires more and detailed data about the longevity of passive, humoral or cellular, immunity. We investigated the humoral immunogenicity of BNT162b2 mRNA vaccine in healthcare workers (HCW) up to 12 months. This study was designed to evaluate the kinetic of antibody response measuring sequential anti-S IgG levels. Participants were voluntary and SARSCoV- 2 naive HCWs of IRCCS Policlinico San Martino Hospital (Genoa, Italy) that they were immunized with two doses of vaccine at December 2020 and a booster dose 9 months later. Blood was sampled prior to vaccine (T0), at 21 days (T1) and 28 days (T2) after the first dose, at 1 (T3), 3 (T4), 6 (T5) and 9 months (T6) after full vaccination, at 1 (T7) and 3 months (T8) after a booster dose. Serological assays were performed at Laboratory Medicine of our hospital using SARS-CoV-2 IgG panel (Bio-Rad, Marnes-la-Coquette, France). It is a multiplex panel of immunoassays intended for the semiquantitative detection of four different IgG antibodies against the receptor-binding domain (RBD), spike 1 (S1), spike 2 (S2) and nucleocapsid (N) structural proteins of SARS-CoV-2. 51 subjects were enrolled among all HCWs and overall, they showed a seroprevalence of 96% (49/51) for RBD and S1 at T1 and 100% (51/51) from T2 to T6. Median values of RBD [100 (51-188) vs 2945 (1693-5364) U/ mL] and S1[79 (30.7-131) vs 1574 (833-3256) U/mL] increased remarkable from T1 to T2. These parameters reduced gradually from T3 to T6 reaching a fold decrease of -20 times (CI 95%: 18-23) and -19 (CI 95%: 17-22) for RBD and S1, respectively. At T7, it was observed an increase of antibody level in comparison to T2 (RBD 4 times, CI 95%: 2,5-6;S1 3 times, CI 95%: 1,5-5). All subjects were negative for anti-N IgG from T0 until to T8. HCWs experienced SARS-CoV-2 infection documented by a molecular or antigen assay for 39,2% (20/51) after a median time of 165 (69-184) days.Naive and healthy people show a protective humoral response with BNT162b2 that it endures up to 12 months with a booster dose at 9th month. Based on the rapid spread of Omicron variants, humoral decrease and booster breakthrough after less of 6 months, an update of vaccine sera booster may be planned for HCWs and patients with failty.