Background: As vaccination against coronavirus disase-19 (COVID-19) evolves, hesitancy has become a problematic issue that has gradually spread worldwide. The main reason for vaccine hesitancy is uncertainties about vaccine side effects. Aims: To evaluate the safety of an inactivated COVID-19 vaccine, CoronaVac, and determine the risk factors of emergence of side effects. Study Design: Cross-sectional study. Methods: An online questionnaire was administered via the internet to healthcare workers who received one or two doses of CoronaVac. The online survey consisted of three sections detailing sociodemographic data, COVID-19 history, and post-vaccine side effects. Side effects that occurred in the period starting from immediately after the first vaccination to the end of the 14th day after the second vaccination were recorded. Results: A total of 1628 healthcare workers responded to the online survey. Of these, 24.3% had a side effect either after the first or second dose of CoronaVac. Redness and/or pain at the inoculation site, headache, muscle and joint pains, palpitations, and dizziness were the most common side effects. Female sex, age <50 years, and thyroid disorder in the pre-vaccine period were found to be risk factors for the emergence of side effects. Blood pressure control could not be achieved in 2.2% of participants despite medication use, and permanent medication was needed in 2.5% of participants for blood pressure control. Conclusion: Almost a quarter of healthcare workers have at least one side effect after the first or second dose of CoronaVac. Female gender, age <50 years, and thyroid disorder appear to be risk factors for the occurrence of side effects.