Incidence of adverse events following COVID-19 vaccination in observational studies
4 affiliations
- 1Graduate Program in Nursing (PPGENF), School of Nursing, Federal University of Alfenas (UNIFAL-MG)
- 2School of Medicine (FAMED), Federal University of Alfenas (UNIFAL-MG)
- 3Federal University of Pelotas (UFPel)
- 4Graduate Program in Biological Sciences, Department of Pathology and Parasitology, Federal University of Alfenas (UNIFAL-MG)
Abstract
Introduction This systematic review and meta-analysis aimed to estimate and synthesize real-world incidence measures of adverse events following immunization (AEFI) associated with COVID-19 vaccines and to examine how methodological and epidemiological factors influence reported estimates. Methods Following PRISMA 2020 guidelines and a prospectively registered protocol (PROSPERO), eight data sources including grey literature were searched for observational studies reporting AEFI incidence in the general population. A total of 160 studies met inclusion criteria. Incidence metrics were grouped by unit of analysis: events per notification, per exposed individual, per 100 doses, and cumulative incidence of individuals experiencing at least one AEFI. Subgroup analyses evaluated variation by age group, vaccine platform, number of doses, data source, study design, and denominator type. Risk of bias was assessed using the JBI tools and ROBINS-I. Results Pooled estimates differed according to metric definition. Event-to-exposure ratios yielded a combined estimate of 0.118 (95% CI: 0.066–0.211; 154 studies), whereas cumulative incidence proportions yielded 0.561 (95% CI: 0.336–0.763; 6 studies). Heterogeneity was extreme (I² ≥ 99%), partly reflecting denominator type: ratios ranged from 0.002 (notification-based) to 0.378 (dose-based) (p < 0.001). Most studies had moderate-to-high risk of bias; excluding high-risk studies reduced the Set 1 estimate by approximately 41% to 0.069 (95% CI: 0.033–0.146). Conclusions Real-world AEFI incidence varies according to the epidemiological metric, denominator structure, and methodological quality of primary studies; event-to-exposure ratios and cumulative incidence proportions capture distinct dimensions of AEFI occurrence and should not be directly compared.
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BibTeX
@article{nascimento2026incidence,
title = {{Incidence of adverse events following COVID-19 vaccination in observational studies}},
author = {Murilo César do Nascimento and Kadja Emanuelle Monteiro Lima and Marcela Emanuelly Silva and Victoria Bicalho Lanza and Isabele Masson de Brito and Vittória de Campos Galo and Ana Laura Silva Nascimento and Felipe Mendes Delpino and Livia Maris Ribeiro Paranaiba Dias},
journal = {Discover Public Health},
year = {2026},
month = oct,
doi = {10.1186/s12982-026-03094-4},
url = {https://doi.org/10.1186/s12982-026-03094-4},
note = {CC BY},
}
RIS
TY - JOUR
TI - Incidence of adverse events following COVID-19 vaccination in observational studies
AU - Murilo César do Nascimento
AU - Kadja Emanuelle Monteiro Lima
AU - Marcela Emanuelly Silva
AU - Victoria Bicalho Lanza
AU - Isabele Masson de Brito
AU - Vittória de Campos Galo
AU - Ana Laura Silva Nascimento
AU - Felipe Mendes Delpino
AU - Livia Maris Ribeiro Paranaiba Dias
PY - 2026
DA - 2026/10/25
JO - Discover Public Health
DO - 10.1186/s12982-026-03094-4
UR - https://doi.org/10.1186/s12982-026-03094-4
AB - Introduction This systematic review and meta-analysis aimed to estimate and synthesize real-world incidence measures of adverse events following immunization (AEFI) associated with COVID-19 vaccines and to examine how methodological and epidemiological factors influence reported estimates. Methods Following PRISMA 2020 guidelines and a prospectively registered protocol (PROSPERO), eight data sources including grey literature were searched for observational studies reporting AEFI incidence in the general population. A total of 160 studies met inclusion criteria. Incidence metrics were grouped by unit of analysis: events per notification, per exposed individual, per 100 doses, and cumulative incidence of individuals experiencing at least one AEFI. Subgroup analyses evaluated variation by age group, vaccine platform, number of doses, data source, study design, and denominator type. Risk of bias was assessed using the JBI tools and ROBINS-I. Results Pooled estimates differed according to metric definition. Event-to-exposure ratios yielded a combined estimate of 0.118 (95% CI: 0.066–0.211; 154 studies), whereas cumulative incidence proportions yielded 0.561 (95% CI: 0.336–0.763; 6 studies). Heterogeneity was extreme (I² ≥ 99%), partly reflecting denominator type: ratios ranged from 0.002 (notification-based) to 0.378 (dose-based) (p < 0.001). Most studies had moderate-to-high risk of bias; excluding high-risk studies reduced the Set 1 estimate by approximately 41% to 0.069 (95% CI: 0.033–0.146). Conclusions Real-world AEFI incidence varies according to the epidemiological metric, denominator structure, and methodological quality of primary studies; event-to-exposure ratios and cumulative incidence proportions capture distinct dimensions of AEFI occurrence and should not be directly compared.
SN - 3005-0774
ER -