Immunogenicity of the BNT162b2 mRNA COVID-19 Vaccine in Elderly People Over 85 Years of Age in Greece

Abstract

Real world data regarding the effectiveness and safety of the new COVID-19 vaccines in older people are currently lacking. The over-85 age group was the first group to receive the BNT162b2 mRNA COVID-19 vaccine in Greece according to the national priority vaccination scheme. The aim of the study was to enhance insight into the antibody generation elicited by the BNT162b2 mRNA COVID-19 vaccine among elderly people over age 85. The immunogenicity was measured using the SARS-CoV-2 IgG II Quant assay to conduct a qualitative and quantitative determination of IgGs against the receptor-binding domain (RBD) of the S1 subunit of the SARS-CoV-2 spike protein on day 21 after the first dose and day 21 after the second dose. In the first phase of our study, antibody levels were monitored in a total of 400 participants while our final sample consisted of 297 subjects since 103 vaccinees did not show up for the second antibody measurement 21 days after the second dose. First dose response was accounted to 69.75% (95%CI: 65.25,74.25) of the subjects and second dose response to 98.99% (95%CI: 97.85, 100). No significance difference between gender was observed (p=0.311). Overall, an impressive 40-fold change was observed between the two doses however, values are plateauing for higher titer levels after 1st dose. Subjects with low response levels after the first dose have significantly higher changes than subjects with initially high response levels. Comorbidities did not seem to affect antibody responses, with the exception of vaccinees with heart disease in whom significantly lower antibody titers were recorded after the first dose, compared to those with a negative history. Concluding, our study highlighted the high foldchange (41.18) recorded in the titers of neutralizing antibodies after the second dose suggesting the need for its timely administration to the elderly individuals. Further studies are needed to better understand the immune response of this population and to determine the duration of the antibody response.