Objective To describe the incidence of adverse events following immunisation (AEFI) and determine the factors that affect the onset and duration of AEFI after COVISHIELD vaccination among healthcare workers.Design Prospective cohort study.Setting Tertiary healthcare, Korle-Bu, Ghana.Participant Three thousand and twenty-two healthcare workers at least 18 years of age were followed up for 2 months after receiving two doses of the COVISHIELD vaccine.Primary outcome The occurrence of the AEFI was identified by self-reporting to the AEFI team members.Results A total of 3022 healthcare workers had at least one AEFI (incidence rate of 706.0 (95% CI 676.8 to 736.1) per 1000 doses) with an incidence rate of 703.0 (95% CI 673.0 to 732.0) per 1000 doses for non-serious AEFI and an incidence rate of 3.3 (95% CI 1.6 to 6.1) per 1000 doses for serious AEFI. The most commonly reported systemic adverse events were headache (48.6%), fever (28.5%), weakness (18.4%) and body pains (17.9%). The estimated median time to onset of the AEFI following the first-dose vaccination was 19 hours and the median AEFI duration was 40 hours or 2 days. Delayed-onset AEFI occurred in 0.3% after first dose and 0.1% after second dose. Age, sex, previous SARS-CoV-2 infection, history of allergies and comorbidity were not significantly associated with the onset and duration of AEFI. However, participants who used paracetamol seemed to be significantly protected (HR 0.15; 95% CI 0.14, 0.17) from having a long duration of AEFI.Conclusion The results of our study indicate a high incidence of non-serious AEFI and the rare occurrence of serious AEFI after COVISHIELD vaccination in healthcare workers. The rate of AEFI was higher after the first dose than after the second dose. Sex, age, previous SARS-CoV-2 infection, allergies and comorbidity were not significantly associated with the onset and duration of AEFI.
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