Objective: Vaccines are an effective war strategy against COVID-19. The success of a large number of vaccines and the continued development of vaccines have significantly affected the course of the current pandemic. The aim of the study is to determine the type and frequency of side effects caused by mRNA vaccine administration to 12 years and older people during the COVID-19 pandemic.

Materials and Methods: The prospective study was conducted among people who applied to a university hospital COVID-19 Vaccination Outpatient Clinic in Eastern Turkey, and they had not previously been vaccinated against COVID-19 except for the BNT162b2 vaccine. The number of participants was 391. The data were analyzed by using SPSS 22 program and the Chi-square test was used for statistical analysis.

Results: The mean age of the participants in the study was 30.55±13.20. The frequency of those who reported at least one side effect following two doses of vaccination was 94.4%. The most common local side effects were pain at the injection site and muscle weakness in the same arm, while systemic side effects were fatigue and muscle/joint pain. The relationship between gender and the incidence of adverse effects after the first, second, and total doses of COVID-19 vaccine was significant (p<0.01).

Conclusions: No serious life-threatening side effect was detected with the Pfizer/BioNTech vaccine administered in this study. However, local and systemic side effects such as pain, fatigue, muscle/joint pain, headache and fever frequently occurred. Further studies are needed to examine long-term adverse effects associated with the mRNA vaccine.