Preliminary Assessment of the Safety and Effectiveness of the Live Attenuated Dengue Vaccine in the First Seasonal Period After Its Introduction in Sus, Brazil, 2024

To evaluate preliminary safety and effectiveness data for the live attenuated dengue vaccine during the first seasonal period after its introduction in SUS. Descriptive-analytical study with linkage of records from the RNDS (vaccination) and SINAN (dengue notifications) between 01/01 and 10/08/2024, in municipalities selected for vaccination of the 10–14-year age group in Brazil. Clinical closure classifications were analyzed (dengue without warning signs (A/B), dengue with warning signs and severe dengue) and laboratory positivity (PCR/NS1) in windows <30 or ≥30 days after each dose (D1 and D2). Safety was evaluated by comparing the proportions of cases with warning signs between groups, using Fisher’s exact test. Vaccine effectiveness (VE) after two doses (≥30 days) was estimated using a test-negative design. A total of 2,215,178 doses were administered and 469,687 notified cases with completed closure were recorded. Of these, 64.4% were dengue A/B, 1.3% dengue with warning signs and 0.05% severe; 34.3% were discarded cases. The proportion of cases closed as dengue was 65.7% (n=303,353) among unvaccinated individuals, 65.3% (n=3,361) among those vaccinated <30 days after D1, 58.6% (n=2,094) ≥30 days after D1, 61.5% (n=59) <30 days after D2 and 41.7% (n=10) ≥30 days after D2. Among unvaccinated individuals, 98.0% were dengue A/B, 1.9% with warning signs and 0.07% severe; among those vaccinated <30 days after D1, 97.6% were A/B, 2.3% with warning signs and 0.1% severe; among those vaccinated ≥30 days after D1, 98.7%, 1.3% and 0.05%, respectively. After two doses, only dengue A/B cases were observed. Fisher’s test did not indicate a significant difference in severity between groups (p=0.17). Regarding the laboratory criterion, 21.6% (n=111,530) were PCR/NS1 positive among unvaccinated individuals and 2.6% (n=1) among those vaccinated ≥30 days after D2. There were 130 deaths among notifications: 48 attributed to dengue (47 in unvaccinated individuals and one <30 days after D1), 57 to other causes and 25 under investigation. The estimated VE for the complete schedule was 36.6% and 88.1%, based on clinical closure classifications and laboratory criteria, respectively. Preliminary data suggest a favorable safety profile, with no increase in clinical severity among vaccinated individuals in the first year of incorporation into SUS. VE should be interpreted with caution given the small number of cases with complete schedules and the context of the end of the seasonal period. The current co-circulation of serotypes reinforces the importance of pharmacovigilance.