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 has been declining in many countries during the COVID-19 pandemic. Bosnia and Herzegovina is no exception. We evaluated a tele-phone-based outreach intervention implemented in primary healthcare facilities (PHCs) in the Federation of Bosnia and Herzegovina. The intervention aimed to target missed routine vaccinations among children aged 0-7 years. Method: By using a programmatic, non-randomized pre-post design, healthcare teams reviewed registries to identify un-der-vaccinated children. Parents were contacted by phone to facilitate catch-up visits. Re-sults: 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 vac-cination 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 rou-tine childhood vaccination coverage in real-world settings and may be a scalable ap-proach for decentralized health systems recovering from pandemic disruptions.