International Journal of Health Sciences Available online at www.sciencescholar.us Vol. 6 No. 1, April 2022, pages: 160-173 e-ISSN: 2550-696X, p-ISSN: 2550-6978 https://doi.org/10.53730/ijhs.v6n1.3626 160 Adverse Events Following Immunization Post Moderna (mRNA- 1273) Booster Vaccination After Two Primary Doses of CoronaVac Irzal Rakhmadhani a , Erna Yulida b , Akhmad Fauzan c , Abdul Kadir Jaelani d Manuscript submitted: 4 September 2021, Manuscript revised: 9 December 2021, Accepted for publication: 5 January 2022 Corresponding Author d Abstract 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. Keywords booster vaccination; COVID-19; health care; health profession; immunization; post moderna; International Journal of Health Sciences © 2022. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/). Contents Abstract ............................................................................................................................................................................................................ 160 1 Introduction ............................................................................................................................................................................................ 161 2 Materials and Methods ...................................................................................................................................................................... 163 3 Results and Discussions .................................................................................................................................................................... 163 a District Health Office of Hulu Sungai Utara, South Kalimantan, Indonesia b District Health Office of Hulu Sungai Utara, South Kalimantan, Indonesia c District Health Office of Hulu Sungai Utara, South Kalimantan, Indonesia d Universitas Sebelas Maret, Surakarta, Indonesia