This study aims to investigate the prevalence of Adverse Events Following Immunization infection among health workers in the Hulu Sungai Utara Regency following two doses of CoronaVac. The study takes a descriptive research method. This research data is taken from two hundred fifty-eight individuals who indicated their willingness to participate in the study. 99 health workers (38.37%) had a history of AEFI at the first and second doses, with symptoms of malaise (36.36%), local pain (32.32%), and fever (22.22%) with an onset of 1–5 days (24.81%), and the majority did not require treatment (72.48 %). The study results showed that almost all health care professionals developed AEFI, both local and systemic, following the third immunization dosage. 257 health care workers (99.6 %) reported experiencing local AEFIs, with pain (95.35 %), swelling (37.60 %), and a red rash (37.60 %). Systemic AEFI was diagnosed in 239 health care workers (92.63 %), with the most common systemic reaction being arthralgia, myalgia (70.54 %), fever (62.02 %), and malaise (38.37 %). The response length was between 1 and 5 days (74.03 %), and 195 health workers (75.58 %) took NSAIDs to alleviate the reaction.