Leave no one behind: Global Analysis on monitoring childhood vaccination timeliness and catch-up using data from the WHO/UNICEF joint reporting form on Immunization.

In the years following the Covid-19 pandemic, immunization programmes have increasingly focused on the capacity to conduct and monitor catch-up vaccination-for doses administered later than the recommended schedule. However, it is unclear whether information systems are able to monitor delayed vaccination. We analyzed WHO/UNICEF Joint Reporting Form data from 194 countries (2016-2022) to understand if systems for tracking delayed childhood vaccination are available and quantify catch-up doses of the first dose of a measles-containing vaccine (MCV1). For Latin American and Caribbean countries, we also explored data for the third dose of diphtheria-tetanus-pertussis vaccine (DTP3). We assessed the completeness and consistency of reporting, the proportion of delayed doses, and vaccination coverage considering both timely and delayed administration. Analyses were disaggregated by WHO Region, World Bank income classification, and Gavi support eligibility. Results show substantial variability across regions and income groups in countries' ability to capture delayed doses. Between 2016 and 2022, the proportion of countries reporting a system to record delayed doses ranged from 55.5% to 64.4% annually, with the Region of the Americas (AMR) consistently reporting a higher proportion (77.1%-82.9%). Among countries with available data, the median proportion of delayed MCV1 doses was 4.4%, suggesting that including catch-up doses in cohort monitoring would increase reported coverage by approximately 4 percentage points. This increase was smaller in Gavi-eligible countries compared with non-eligible countries. The study summarizes global differences in information systems to monitor catch-up vaccination, presents examples of cohort coverage monitoring and illustrates the need to further improve immunization information systems and explore the potential for improving vaccination coverage and population immunity through catch-up activities.