Immunogenicity after the First Dose of the BNT162b2 mRNA COVID-19 Vaccine: Real-World Evidence from Greek Healthcare Workers

Abstract

Background: The BNT162b2 mRNA Covid-19 vaccine that was recently launched exhibited high levels of efficacy and safety in a phase III RCT, along with robust immunogenicity in phase II trials. However, the release of phase IV studies verifying these preliminary findings by means of real-life evidence is essential.

Methods: We measured titers of neutralizing IgGs against the receptor-binding domain (RBD) of the S1 subunit of the spike protein of SARS-CoV-2 14 days post-immunization of 425 healthcare providers utilizing the SARS-CoV-2 IgG II Quant assay and estimated the geometric mean concentration (GMC) of SARS-CoV-2-specific IgGs both in the previously-infected group and among the uninfected. The trial is registered on the International Standard Randomized Controlled Trial Number registry (study ID: ISRCTN61884303).

Results: 392 of study participants 92.24% (95% CI:89.27, 94.43) had a positive SARS-CoV-2 IgG II Quant assay, while 33 subjects had an IgG concentration lower than 50 AU/ml (GMC 24.80303 AU/ml; 95% CI:19.190, 30.41612). All 63 previously-infected convalescent participants had very high SARS-CoV-2-specific antibody titers with a GMC of 19993,61AU/ml. Regarding age, antibody titers did not significantly differ in the range of 20-50 years, being however significantly lower in the 50-60 age group and dropping even further in subjects over the age of 60. Adverse reactions were overall mild, including pain at the site of the injection, fatigue, myalgias, headache and chills. No serious adverse events were reported in this study.

Conclusion: To our knowledge, this is the first phase IV study in Greece presenting real-world evidence on the immunogenicity of the first dose of the BNT162b2 mRNA Covid-19 vaccine in a sample of 425 healthcare providers.

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

Funding: None.

Declaration of Interests: None to declare.

Ethics Approval Statement: The study protocol was approved and ethical approval was obtained by the ethics committee of the scientific council of the G. Gennimatas General Hospital (protocol number:1/13.1.2021).

Keywords: vaccine, BNT162b2, SARS-CoV-2, immunogenicity, healthcare workers, Greece, reactogenicity