COVID-19 vaccine safety studies among special populations: A systematic review and meta-analysis of 120 observational studies and randomized clinical trials.
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BACKGROUND: The COVID-19 vaccines were rapidly developed and tested, but concerns about vaccine-related adverse events remain, especially in special groups like pregnant women, children, and those with certain health conditions. This review aims to summarize rates of such adverse events in individuals often not included in randomized clinical trials (RCT). METHOD: From December 2019 to February 2022, we searched Embase and Medline for observational studies and RCTs on adverse events post-COVID-19 vaccination in special populations. We examined severe and non-severe events in individuals with specific medical conditions, infants, children, pregnant individuals, and socioeconomically disadvantaged individuals. Cumulative risks for all events were calculated. The Incidence rate (IR) and 95% confidence intervals were reported for those studies that met the follow-up period criteria based on the referenced literature. For events with data on exposed and unexposed groups, we calculated the odds ratio (OR). Pooled incidence rates were calculated per 1000,000 person-days using a random-effects model. Sub-group analyses were conducted based on vaccine types and doses, with heterogeneity assessed using I2. RESULTS: Of the 4,254 papers, 235 met eligibility criteria, including 120 studies with 171,073 participants (113 observational, eight RCTs). We examined 17 severe and seven non-severe adverse event categories. Lymphadenopathy (IR: 1950[1200,3190]), autoimmune disease and multiple sclerosis flare-up (1130 [470,2680]), and cardiac symptoms (0.26[0.00,10.58]) were the most prevalent severe adverse events. Autoimmune disease flare-ups and cardiac symptoms were more common following the second dose compared to the first dose. The overall incidence of serious adverse events was low in children and adolescents, pregnant, autoimmune, and cancer patients. DISCUSSION: This review highlights COVID-19 vaccine safety in special populations, enhancing vaccination strategies. Further real-world research is needed to validate and extend our findings, especially in addressing safety gaps among special groups.