Vaccination Coverage: Why Can National Averages Mislead?

Why can national vaccination averages hide local risks?

WHO estimates that 85% of infants worldwide received three doses of a diphtheria, tetanus and pertussis-containing vaccine in 2025. First-dose measles coverage reached 84%, while 13.5 million infants missed their initial DTP dose. These figures describe different vaccination indicators, rather than the proportion of children protected against every vaccine-preventable disease. They also cannot show how evenly vaccination is distributed within individual countries. [WHO immunization coverage fact sheet](https://www.who.int/en/news-room/fact-sheets/detail/immunization-coverage).

WHO explicitly warns that national coverage figures can conceal substantial inequalities within countries. A strong result in one district can offset a weak result elsewhere in the national calculation. For health services, that distinction matters: an average cannot identify which communities need additional appointments, outreach or follow-up. District-level monitoring helps make those differences visible. [WHO subnational immunization coverage data](https://www.who.int/teams/immunization-vaccines-and-biologicals/immunization-analysis-and-insights/global-monitoring/immunization-coverage/subnational-immunization-coverage-data).

This challenge illustrates the continuing relevance of WHO's SCORE health-data package, originally announced on August 27, 2020. Developed in the context of COVID-19, the framework promotes reliable, comparable information and its use in health decisions. Applying that principle to vaccination means examining who is missing services behind an apparently reassuring headline percentage. [WHO's original SCORE announcement](https://www.who.int/news/item/27-08-2020-new-who-technical-package-health-data-for-covid-19-response).

How can vaccination coverage estimates become inaccurate?

Calculating coverage requires both a count of vaccinations and a reliable estimate of the population eligible for that particular dose. Missing reports can lower the recorded vaccination count, while recording errors can inflate it. An outdated estimate of how many children live in an area can distort the percentage even when clinics accurately report their work. WHO and UNICEF therefore assess administrative records alongside surveys and information from local experts when producing national estimates. [WHO/UNICEF coverage estimation methods](https://www.who.int/news-room/questions-and-answers/item/who-unicef-estimates-of-national-immunization-coverage).

Coverage reported above 100% is a particularly clear warning that the recorded vaccinations and estimated target population do not align. WHO identifies such results, erratic annual changes and outbreaks in supposedly well-vaccinated areas as reasons to examine population estimates. These warning signs warrant investigation; they do not establish the cause of an error on their own. [WHO guidance on target population estimates](https://www.who.int/publications/m/item/assessing-and-improving-the-accuracy-of-target-population-estimates-for-immunization-coverage).

Household surveys provide another perspective, but they also have limitations. Some difficult-to-reach communities may be excluded, and missing vaccination cards can leave researchers dependent on caregivers' memories. WHO notes that recalled vaccination histories are less reliable than documented records. Agreement between several information sources is therefore more reassuring than an apparently precise percentage from one incomplete dataset. [WHO/UNICEF explanation of data limitations](https://www.who.int/news-room/questions-and-answers/item/who-unicef-estimates-of-national-immunization-coverage).

How can better local data improve childhood vaccination?

WHO's subnational monitoring collects information on first and third DTP doses and first measles doses, alongside the populations eligible to receive them. Looking at these indicators separately helps services examine both initial contact and completion of a vaccine series. WHO recommends using local coverage patterns to focus interventions where access is weakest. However, the figures need quality checks before they guide decisions about staffing, supplies or outreach. [WHO subnational monitoring framework](https://www.who.int/teams/immunization-vaccines-and-biologicals/immunization-analysis-and-insights/global-monitoring/immunization-coverage/subnational-immunization-coverage-data).

The practical implication is that finding a coverage gap should begin an investigation into its cause. A low figure might reflect missed vaccinations, incomplete reporting or an inaccurate population estimate, each requiring a different response. Better information can guide action, but collecting it alone does not demonstrate that more children have been vaccinated. SCORE's emphasis on reviewing information and using it in decisions provides a useful framework for connecting measurement with service improvement. [WHO SCORE framework](https://www.who.int/news/item/27-08-2020-new-who-technical-package-health-data-for-covid-19-response).