Objectives: Although clinical data have shown that the BNT162b2 vaccine, which is widely used in many countries, is safe and effective as a protection against the SARS-CoV-2 infection, extant research in adverse reactions using real-world data of various sociodemographic characteristics is scant. Methods: We conducted a prospective cohort study to compare age differences in self-reported reactogenicity of BNT162b2 in Hong Kong. A total of 1,516 participants were intensively followed up for two weeks following both doses of BNT162b2 vaccination, during which their basic demographic, health conditions, and medication information were collected. Results: Results from the generalized mixed model showed that compared with adults aged 18 to 59 years, older adults aged 60 years or above had a lower risk of adverse reactions and adolescents aged 12 to 17 years had a moderately higher risk. Conclusions: Results of this study should be informative to parents considering BNT162b2 vaccination for their children in that moderately increased reactogenicity compared with adults is anticipated.