Evaluation of Side Effects After Heterologous Vaccination with BNT162b2 Vaccine in Healthcare Workers Vaccinated with Two Doses of Inactive COVID-19 Vaccine

Objective: Vaccination is the most effective way to control the COVID-19 pandemic all over the world. We aimed to evaluate the relationship between antibody titers and vaccine side effects after the BNT162b2 vaccine was administered as a reminder dose in healthcare workers (HCW) who received two doses of inactivated SARS-CoV-2 vaccine name CoronaVac (Sinovac Life Sciences, Beijing, China).Methods: A total of 428 HCWs participated in the study. Participants who received the mRNA vaccine as a reminder dose were evaluated with a questionnaire regarding antibody values and vaccine side effects. Three weeks after the first BNT162b2 vaccine, the same questionnaire was applied face-to-face to HCW, and the same questionnaire was applied to those who received a second reminder dose via telephone.Results: Out of 428, 373 (87.1%) HCWs preferred one and 55 (12.9%) two doses of the BNT162b2 vaccine as reminder doses after being vaccinated with an inactivated vaccine. It was observed that side effects were more frequent in women aged 18-40 after a single dose of the BNT162b2 vaccine (p<0.001). The most common side effects are redness, swelling, and pain at the injection site, with a rate of 59.6%. Fatigue-weakness was the most common systemic reaction, with a rate of 58.6%. Axillary lymphadenopathy was observed seen in 3 (1.1%) HCWs. The median value of IgG titers in the third week after the reminder dose was found to be higher in HCW with side effects than those without side effects (p<0.001). When the cumulative incidence rate of vaccinated people was evaluated over 389 people, no cases were ob-served on the 14th and 30th days after the first reminder dose of BNT162b2. However, the first case was observed on the 60th day, and after the second reminder dose, cases were seen on the 14th, 30th, and 60th days.Conclusion: Since the side effects detected after the BNT162b2 reminder dose were mild to moderate and progressed with local symptoms, it was concluded that highly protective mRNA vaccines could be safely preferred for protection from COVID-19.