Comparative Health Outcomes of Vaccinated versus Unvaccinated Children: A Retrospective Cohort Analysis

Background/Objectives: The long-term health outcomes of the expanded childhood vaccination schedule remain inadequately characterized. Existing comparative studies have reported elevated risks of neurodevelopmental, allergic, and infectious morbidity among vaccinated children. This study compares health outcomes between vaccinated and unvaccinated pediatric populations using a retrospective cohort design and Pearson chi-square odds ratio calculations. Methods: Electronic medical records from eight U.S. pediatric practices were analyzed for 6,239 children born into the practices with at least one encounter between ages 2 and 4. Vaccination status was dichotomized: at least one vaccine before 13 months versus zero vaccines ever. Nine clinical conditions—developmental delay, rhinitis, breathing abnormalities, nausea/vomiting, ear infection, respiratory disease, skin rash, strep infection, and fever—were assessed via ICD-9/10 codes using minimum frequency thresholds. Odds ratios (OR) and 95% confidence intervals were calculated, along with sex-stratified and dose-response quartile analyses. Results: Vaccination before 13 months was associated with significantly elevated odds of rhinitis (OR 1.8), ear infection (OR 2.0), respiratory disease (OR 1.6), and strep infection (OR 2.3) (all p < 0.001). Developmental delay was not significant overall (OR 0.9) but was significantly elevated in the highest vaccine quartile (10+ vaccines: OR 1.4, p = 0.0031). Strep infection showed a clear dose-response gradient (OR 1.5 to 3.4). Females showed particularly strong associations for strep infection (OR 2.6). Conclusions: Vaccination was associated with significantly increased odds of multiple acute and chronic conditions. These results, consistent with prior comparative literature, underscore the urgent need for independent, adequately powered prospective research comparing vaccinated children to truly unvaccinated controls to fully characterize vaccine-associated pediatric morbidity.