Non-specific effects of MMR vaccines on infectious disease related hospitalizations during the second year of life in high-income countries: a systematic review and meta-analysis

Children who had received MMR as the most recent vaccine had a pooled 35% (95%CI: 12–53%) lower risk for hospitalization due to any infectious disease, compared to children who had received DTaP as the most recent vaccine (three studies, 1,919,192 children). The effect was stronger for respiratory tract infections than for gastrointestinal infections. Two studies investigated MMR alone, compared to concurrent administration of MMR and DTaP vaccines. Here, the pooled estimate for reduction in risk of hospitalization for any infectious disease was smaller and not significant (15%; 95%CI: −9% to 34%). Risk of bias was serious to critical in all studies. Moreover, two of the five studies demonstrated a significantly reduced risk for a control outcome (hospitalization for injuries), strongly indicating healthy vaccinee bias or residual confounding. The available evidence is insufficient to support a change in current vaccination schedules.