Adverse Events and Immunization Errors Following a Mass Immunization Campaignwith TAK‐003 in Dourados, Brazil: <i>A Post‐Marketing Safety Surveillance Analysis</i>

This descriptive observational study based on post-marketing surveillance data evaluates adverse events following immunization (AEFI) associated with the TAK-003 (Qdenga®) vaccine. Conducted in Dourados, Brazil, between January and November 2024, the study aimed to assess the frequency, nature, and severity of AEFI to inform public health strategies. Secondary data were obtained from the e-SUS Notifica system, including demographic information, vaccination dates, and details of AEFI, which encompassed immunization errors and adverse events. These adverse events were classified by severity, type, and temporal distribution. Statistical analysis included incidence rates, temporal trends, and correlation analyses using SPSS software. Among 124,483 administered doses, 88 AEFI were reported, yielding an incidence rate of 70.69 per 100.000 doses. Most events (49.00 per 100.000 doses) were Nonserious, including headache, fever, and rash. Serious AEFI were rare (6.42 per 100.000 doses), with two cases of grade 1 anaphylaxis and two Guillain-Barré syndrome (GBS) cases. Women (71.01%) and individuals aged 30-39 years (82.06 per 100.000 doses) were the most affected. Twenty seven Immunization errors were reported for 30.68% of AEFI, often linked to gaps in training. TAK-003 demonstrated a favorable safety profile, consistent with clinical trial findings, characterized predominantly by mild, self-limiting adverse events, with serious adverse events occurring infrequently. These findings underscore the importance of enhanced training protocols, robust surveillance systems, and timely reporting to optimize vaccine safety and maintain public trust.