Comparison of Hospitalizations in BCG-Vaccinated and Unvaccinated Children in Portugal (2010–2021)

Abstract Background Universal BCG vaccination in Portugal ended in 2016, remaining for high-risk groups. Assessing hospital admissions by BCG status helps understand the impact on pediatric morbidity. Objectives To compare hospitalized children under 5 by BCG status, analyzing differences in frequency, causes, duration, timing, and estimating hospitalization risk. Methods A retrospective cohort study of hospitalized children under 5 born between July 2010 and June 2021 was conducted using national databases. Variables analyzed included vaccination status, admissions, sex, district, and birth year. Associations were tested with chi-square and t-tests. Incidence rates were calculated over 5 years or until 30/06/2021. Children with low birth weight, prematurity, HIV, or abnormal birth (non-DRG 795) were excluded. Results A total of 347,897 hospitalized children were analyzed (235,216 unvaccinated; 112,681 vaccinated). No significant differences in sex (p = 0.51) or district (p = 0.05) were found. Lisbon and Porto had the highest hospitalizations. Among unvaccinated children, 82.4% of admissions occurred during the perinatal period; in vaccinated children, 37.8% occurred after the neonatal period. Regarding causes, perinatal conditions predominated in unvaccinated children (24.8%), and respiratory diseases in vaccinated children (34.0%, p < 0.001). Vaccinated children had slightly more hospitalizations (1.43 vs. 1.41) but shorter average hospital stays (5.02 vs. 5.39 days). Children vaccinated after 2016 received BCG earlier (mean 3.6 days) compared to children from earlier cohorts (>17 days). Hospitalization incidence rates were similar (0.2009 vs. 0.2004 hospitalizations per child-year), with an HR of 0.9975 (95% CI: 0.797-1.248), indicating no significant difference in hospitalization risk between unvaccinated and vaccinated children. Conclusions BCG vaccination may influence morbidity patterns, emphasizing the need for continuous monitoring to support public health strategies. Key messages • Hospitalization risk was similar in BCG-vaccinated and unvaccinated children but causes and timing of admissions varied significantly between groups. • Findings suggest BCG vaccination may influence morbidity patterns, highlighting the need for ongoing monitoring to guide public health decisions.