(328) A Comprehensive Review and Meta-analysis of COVID-19 Vaccine Studies in Vulnerable Populations- Analysis of 126 observational and clinical trials up to November 2022

Background: The global COVID-19 pandemic has prompted vaccine development to combat its spread. Still, concerns arise about adverse events of special interests (AESIs) following vaccination, particularly among vulnerable groups like pregnant women, children, and those with autoimmune, cancer or immunocompromised conditions.

Objectives: To systematically review and summarise the prevalence and incidence rates (IR) of AESIs related to the COVID-19 vaccine in vulnerable individuals, often not included in pivotal clinical trials.

Methods: We searched Embase, Medline, and Google Scholar from December 2019 until November 2022, encompassing observational studies and clinical trials evaluating COVID-19 vaccine safety in vulnerable populations. The focus was on AESIs, categorised as severe and non-severe, as the primary outcomes. We pooled the prevalence and IR of AESIs in the post-vaccination risk window, with rates reported per 1000 person days with a 95% confidence interval. Heterogeneity was assessed using I2, and sub-group analyses were conducted based on vaccine types and doses.

Results: Of the 4,254 papers, 235 met eligibility criteria, including 120 studies with 171,073 participants (113 observational, 8 clinical trials). We examined 17 severe and 7 non-severe adverse event categories. Lymphadenopathy (IR: 1.95 [1.20-3.19]), autoimmune disease and multiple sclerosis flare-up (1.13 [0.47-2.68]), and cardiac symptoms (0.26 [0.00-10.58]) were the top severe events. Allergic reactions were more common among autoimmune diseases (7.03 [4.10-12.06]) and cancer (4.87 [2.21-10.76]) groups. In observational studies, the second vaccine dose was linked to higher proportions of disease flare-ups (39.27 [18.08-85.31] vs. 22.13 [10.22- 47.93]); cardiac symptoms (6.11[2.05-18.22] vs 3.78 [2.53-5.65]); and cardiac events (5.34 [ 1.69-16.90] vs 5.05[1.40, 18.19]) compared to first dose.

Conclusions: This review highlights that autoimmune disease and cancer patients exhibited a heightened IR of severe adverse events compared to other vulnerable populations. This underscores the vulnerability of these populations and emphasizes the necessity for further vaccine studies to address their unique needs..