Adverse events following immunisation of COVID-19 vaccine among health care workers in the first phase of vaccination.

Introduction: The new COVID-19 vaccine was met with worldwide overwhelming uncertainties pertaining to its safety profile, effectiveness, and potential adverse reactions when it was first introduced. This led to vaccine refusal and delay in vaccine uptake in many countries including Malaysia. The objective of this study was to determine the Adverse Events Following Immunization (AEFI) to the COVID-19 vaccine.

Materials And Methods: A retrospective cross-sectional study was conducted among healthcare workers who received the COVID-19 vaccine during the first phase of immunisation from eight public primary clinics in Johor Bahru district. Data were collected between May and September 2021 using a self-administered questionnaire.

Results: A total of 240 healthcare workers participated and all of them received the Pfizer Messenger RNA vaccine. Our study found that a large majority of vaccine recipients (87.5%, n=210) experienced AEFI to COVID-19 vaccine for either the first, second, or both doses. More than 80% of them experienced more than one type of AEFI. The most common AEFI reported during the first and second dose was localised symptom such as pain at injection site (60-68%), pain on the injected arm (52-61%), and swelling at injection site (32-33%). Common systemic symptoms were fever (22- 57%), myalgia (20-45%), and dizziness (24-26%). Although a large majority experienced AEFI, these reactions were mostly of mild to moderate severity (47.3-73.6%). The mean duration of AEFI onset was within 30 minutes to about 1 day (0.33-22.5 hours) of injection and lasted between 30 minutes and 2.5 days. There was no association between demographic characteristic of participants and severity of AEFI to COVID-19 vaccine. Mean duration of fever was significantly (p=0.005) longer after the second dose (34.2 hours) of vaccine compared to first (20.6 hours) CONCLUSION: This study shows that a large majority of COVID-19 vaccine recipients experienced AEFI; however, these reactions were mostly of mild to moderate severity and lasted between 30 minutes and 2.5 days. A large majority experienced more than one type of AEFI. The most common AEFI was localised reactions consisting of pain and swelling at the injection site and pain on the injected arm. The most common systemic reactions were fever, myalgia, and dizziness. Duration of fever was significantly longer after the second dose.