Timeliness of routine childhood vaccination in the Democratic Republic of the Congo: data from national vaccine surveys in 2021/2022, 2023 and 2024

BACKGROUND: While crude vaccine coverage is a frequently reported coverage measure in the Democratic Republic of the Congo (DRC), timeliness of vaccine delivery is comparatively understudied. To achieve full vaccine benefits, both high coverage and timely delivery are required. This analysis investigated the timeliness of childhood vaccinations and associated factors across three national Vaccine Coverage Surveys conducted in 2021/2022, 2023, and 2024 in the DRC. METHODS: We conducted a secondary analysis of vaccination coverage data from 79,761 children aged 12-23 months. Weighted coverages and timeliness among vaccinated children were determined. Time-to-event analyses using Kaplan-Meier curves and multilevel Cox regression models were used to assess trends and predictors of vaccination timeliness. RESULTS: Nationally, crude estimates of complete vaccination coverage were 50.1% (48.5-51.7) in 2021/2022, 55.1% (53.6-56.6) in 2023 and 38.4% (37.1-39.6) in 2024, with timely administration among vaccinated individuals ranging from 17.5% to 51.8%. Timely complete vaccination significantly decreased over time from 23.4% (22.0-24.8) in 2021/2022 to 17.5% (16.6-18.5) in 2024 with substantial variance among provinces and health zones. Children whose mothers/guardians had good knowledge about vaccine preventable diseases (VPDs) were consistently more likely to receive timely vaccines across surveys (aHR = 1.16 (1.08-1.25); aHR = 1.09 (1.02-1.15); aHR = 1.10 (1.02-1.14)) respectively in 2021/2022, 2023 and 2024; while crowded households (with three or more children under five) showed delayed vaccination in 2021/2022 and 2023 (aHR = 0.86 (0.77-0.97); aHR = 0.89 (0.81-0.99) respectively). In 2021/2022, households who reported paying for a vaccination card, or home-based records also reported higher rates of delayed vaccination completion (aHR = 0.87, p = 0.011). CONCLUSION: Timeliness among vaccinated children has declined over time, with data showing worsening trends across three successive survey years. Addressing regional disparities, improving caregiver's health education, and removing financial barriers are essential to enhance coverage and timeliness in childhood immunization.