Second dose of the BNT162b2 mRNA vaccine: Value of timely administration but questionable necessity among the seropositive.

This study monitored titers of neutralizing IgG against the receptor-binding domain of the SARS-CoV-2 S1 subunit 14 days post-injection of each dose of the BNT162b2 mRNA Covid-19 vaccine in 401 Greek healthcare workers aged 20-67. After the first dose, titers varied upon age and history of infection, being lower in the 50+ age group and significantly higher among the seropositive. After the second dose, immunogenicity was significantly boosted in the age 50+ and SARS-CoV-2-naïve individuals, indicating the effectuality of its timely administration, yet questioning its value among the seropositive.