Supplementary Material for the Article: "COVID-19 Vaccine Adverse Events by Country Income Level: A Systematic Review and Meta-Analysis of Randomized Controlled Trials"

This systematic review and meta-analysis synthesized data from 11 randomized controlled trials (7,841 participants) to estimate the incidence of adverse events following COVID-19 vaccination (AEFI) across countries categorized by income level. Studies published between 2020 and 2025 were retrieved from EMBASE, PubMed/MEDLINE, and Scopus. Relative risks were calculated using Mantel-Haenszel random-effects models, and subgroup analyses were performed by dose and income level. AEFI incidence was consistently higher in high-income countries compared to upper-middle-income countries, especially after the second dose. The most common events were injection-site pain, headache, myalgia, and fatigue. Meta-analyses confirmed significantly higher risk ratios for both local and systemic reactions in high-income settings. These findings highlight disparities in post-vaccination experiences and inform equitable surveillance strategies.