Early Adverse Events between mRNA and Adenovirus-Vectored COVID-19 Vaccines in Healthcare Workers

Mass vaccination campaigns are important to control the COVID-19 pandemic, however, adverse events (AEs) contribute to vaccine hesitancy. To investigate and compare early AEs between the BNT162b2 mRNA and AZD1222 adenovirus-vectored vaccines, recipients completed daily surveys about local and systemic reactions for 7 days after each dose, respectively. A total of 80 and 1440 healthcare workers received two doses of BNT162b2 and a first dose of AZD1222 vaccines. Any AEs were reported by 52.5% of recipients after the first dose of BNT162b2, by 76.2% after the second dose of BNT162b2, and by 90.9% after the first dose of AZD1222 (p < 0.001). Younger vaccinees had more AEs after the second dose of BNT162b2 and first dose of AZD1222. Sex based differences were only observed in the AZD1222 recipient group. No incidence of anaphylaxis or neurologic AEs were observed. In conclusion, early AEs were mostly mild to moderate in severity and generally transient in both BNT162b2 and AZD1222 groups. Sufficient explanation of the expected AEs of the vaccine would be helpful for wider vaccination.