Evaluation of S1RBD-Specific IgG Antibody Responses following COVID-19 Vaccination in Healthcare Professionals in Cyprus: A Comparative Look between the Vaccines of Pfizer-BioNTech and AstraZeneca.

There is an ongoing effort to report data on SARS-CoV-2 antibodies in different individuals. Ninety-seven healthcare workers were enrolled in this study (Pfizer's BNT162b2, n = 52; and AstraZeneca's ChAdOx1-S, n = 45) and S1RBD-specific IgG antibodies were analyzed over time. Both vaccines induced S1RBD-specific antibodies after the second dose. A significant increase in S1RBD-specific IgG median levels 3 weeks following the second dose was detected (BNT162b2, 118.0 BAU/mL to 2018.0 BAU/mL; ChAdOx1-S, 38.1 BAU/mL to 182.1 BAU/mL). At 3 months post the second dose, a significant decrease in S1RBD-specific IgG median levels was also evident (BNT162b2, 415.6 BAU/mL, ChAdOx1-S, 84.7 BAU/mL). The elimination rate of these antibodies was faster in BNT162b2- rather than ChAdOx1-S- vaccinated individuals. A booster dose induced a significant increase in the S1RBD-specific IgG median levels (BNT162b2, 1823.0 BAU/mL; ChAdOx1-S, 656.8 BAU/mL). This study is the first of its kind to characterize S1RBD-specific IgG antibody responses in vaccinated healthcare workers in Cyprus. While the positivity for S1RBD-specific antibodies was maintained 3 months after the second vaccine dose, the level of these antibodies waned over the same period, indicating the importance of a booster vaccination. The results herein could complement the public health policies regarding the immunization schedule for COVID-19.