The number of COVID-19 cases has continued to rise since the World Health Organization (WHO) declared the Coronavirus Disease 2019 (COVID-19) as a global pandemic in March 2020. At this time, WHO has received reports of about 460 million confirmed illnesses and over 6 million deaths. In Saudi Arabia, the number of confirmed cases has nearly surpassed 750 thousand, with COVID-19 responsible for approximately 9,000 deaths. Vaccination is the most effective approach to prevent this pandemic, and persons who have had three doses are better protected than those who have not. The goal of this study is to look into the adverse effects of COVID-19 vaccine after the third booster dosage in Saudi Arabian healthcare personnel. Between November 2021 and April 2022, a cross-sectional survey was conducted using simply a questionnaire. Pain at injection site was the commonest side effect, followed by fatigue and headache. There is a temperature and edema at the injection site, respectively. 27.71 percent of female participants experienced menstrual cycle changes such as delayed or menorrhagia. The side effects are comparable to those experienced after the first and second COVID-19 vaccination doses. More research on long-term side effects, as well as studies into the relationship between menstrual cycle changes and COVID-19 vaccination, is needed.