Improving Routine Childhood Vaccination Coverage Through Registry-Driven Telephone Outreach: A Large Pre–Post Study from the Federation of Bosnia and Herzegovina

Background: Vaccination coverage declined in many countries during the COVID-19 pandemic, including in Bosnia and Herzegovina. We evaluated a telephone-based outreach intervention implemented in primary healthcare facilities (PHCs) in the Federation of Bosnia and Herzegovina. The intervention targeted missed routine vaccinations among children aged 0–7 years. Method: Using a programmatic, non-randomized pre–post design, healthcare teams reviewed registries to identify under-vaccinated children, and parents were contacted by phone to facilitate catch-up visits. Results: Among age-eligible children, vaccination coverage increased from 66.5% to 74.2% for measles–mumps–rubella (MMR) dose 1, from 43.4% to 51.7% for MMR dose 2, and from 50.4% to 55.9% for the fourth dose of diphtheria–tetanus–acellular pertussis-inactivated poliovirus–Haemophilus influenzae type b vaccine (DTaP-IPV-Hib). Mixed-effects models adjusting for age, sex, and clustering by facility and canton showed higher odds of vaccination post-intervention for MMR dose 1 (adjusted odds ratio [aOR] 1.65), MMR dose 2 (aOR 1.61), and DTaP-IPV-Hib dose 4 (aOR 1.39; all p < 0.001). Conclusions: These results show that registry-based, proactive outreach can yield significant improvements in routine childhood vaccination coverage in real-world settings and may be a scalable approach for decentralized health systems recovering from pandemic disruptions.