Study Design and Participants
The study was conducted in three centers (Koç University Hospital, Istanbul University Cerrahpasa Hospital, and Istanbul University, Istanbul Medical School Hospital ) in Istanbul. Individuals who had two doses of CoronaVac and no history of COVID-19 were included in the study. The baseline blood samples were collected three to five months after 2 doses of CoronaVac. Follow-up samples were taken one and three months after the third dose of CoronaVac or one dose of the mRNA BNT162b2 vaccine (Figure 1). All the individuals were followed up for SARS-CoV-2 infection. Sampling was approved by The Institutional Review Board of Koç University with the number of 2021. 151.IRB1.055.
A total of 52 individuals received two doses of CoronaVac and whole blood samples were collected 3-5 months after vaccination. (n= 19 for 3 months, n=26 for 4 months, n=7 for 5 months.) One month after receiving the 3rd dose (booster) vaccine, whole blood samples were collected from the same 52 individuals. (n=42 for BNT162b2 and n=10 for CoronaVac) . Because of changed vaccine recommendations due to variant of concerns, some volunteers received the 4th dose of BNT162b2 or CoronaVac vaccine, therefore excluded from the study. Therefore, six participants from the BNT162b2 booster group and four participants from the CoronaVac booster group donated blood samples 3 months after the booster dose.