Second Dose of the BNT162b2 mRNA Vaccine in Greece: The Value of Timely Administration

Abstract

Aim: Our study aimed to assess the generation of neutralizing antibodies elicited 14 days post-injection of each dose of the BNT162b2 in 401 Greek healthcare workers, 59 of whom were previously-infected.

Methods: The SARS-CoV-2 IgG II Quant assay on the Architect System was employed to monitor titers of neutralizing IgG against the receptor-binding domain of the S1 subunit of the spike protein in participant-derived serum samples.

Results: After the first dose, titers were found to fluctuate with age, marking a significant decline in the 50-60 age group, while dropping even further in participants aged over 60. This difference was surmounted following the second dose, as the fold-changes recorded were significantly higher in the 50-60 age group, while escalating in subjects aged over 60. After the second dose, the respective fold-change reached significance only among the uninfected, while being marginal in the seropositive group. The immune response of previously-infected subjects to the first dose was more intense than the respective response of the uninfected to the second dose.

Conclusion: Our findings suggest the importance of the timely administration of the second dose in the wide age range of 20-67 of our study cohort, questioning however its value among the seropositive.

Note: Trial Registration: The trial is registered on the International Standard Randomized Controlled Trial Number registry (study ID: ISRCTN61884303).

Funding Statement: None.

Declaration of Interests: None to declare.

Ethics Approval Statement: The study protocol was reviewed and approved by the Scientific Committee of the “G. Gennimatas” General Hospital (protocol number:1/13.1.2021).

Keywords: BNT162b2 mRNA vaccine, immunogenicity, seropositive, Greece