Objectives This article aims to summarize the 6-month variation of a vast array of anti-SARS-CoV-2 antibodies in recipients of BNT162b2 mRNA-based vaccination. Methods The study population consisted of 84 baseline SARS-CoV-2 seronegative healthcare employees (median age 45 years, 53.6% females), receiving mRNA-based BNT162b2 primary vaccination cycle. Blood was collected before the first and second BNT162b2 vaccine doses, as well as 1, 3 and 6 months afterwards. The serum titers of the following anti-SARS-CoV-2 antibodies were assayed: total anti-RBD (receptor binding domain), anti-spike trimeric IgG, anti-RBD IgG and anti-spike S1 IgA. Results All antibodies’ levels peaked 1 month after vaccination, but then displayed a considerable decrease. The median rates of 6-month decline were −95% for IgG anti-SARS-CoV-2 RBD, −85% for IgG anti-SARS-CoV-2 trimeric spike, −73% for IgA anti-SARS-CoV-2 S1 and −56% for total anti-SARS-CoV-2 RBD antibodies, respectively. The median time of seronegativization was estimated at 579 days for total anti-SARS-CoV-2 RBD antibodies, 271 days for IgG anti-SARS-CoV-2 trimeric spike, 264 days for IgG anti-SARS-CoV-2 RBD and 208 days for IgA anti-SARS-CoV-2 S1, respectively. The rate of seropositive subjects declined from 98–100% at the peak to 50–100% after 6 months. The inter-individual variation of anti-SARS-CoV-2 antibodies reduction at 6 months was 3–44% from the peak. Conclusions The results of this longitudinal serosurvey demonstrate that the titer of anti-SARS-CoV-2 antibodies declined 6 months after BNT162b2 vaccination, with median time of IgG/IgA seronegativization estimated between 7 and 9 months, thus supporting the opportunity of administering vaccine boosters approximately 5 to 6 months after the last dose of the primary vaccination cycle.
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