The kinetics of postvaccination serum anti-Spike IgG concentration were determined in 1,541 health care workers (Sant'Andrea Hospital of Rome, Italy) with no prior infection by SARS-COV-2. Anti-Spike IgG were measured at 3, 12, and 24 weeks after the completion of the primary vaccine cycle (two doses of the BNT162b2 vaccine by Biontech/Pfizer) and 3 weeks apart a third BNT162b2 dose. Stratification of the study population by age (decades from 21-30 to 61-70) highlighted that 24 weeks after cycle completion all age groups had an order of magnitude reduction in serum IgG titers. Considering older adults (age 61-70), they had significantly lower serum IgG titers at each time point compared with younger people, except after the booster dose, which induced similar and elevated IgG titers despite the age.
Keywords: BNT162b2 vaccine; COVID-19; booster COVID-19 vaccination; elderly; postvaccination humoral response.