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Current #immunization programs primarily track vaccination coverage (the percentage of children vaccinated), but this metric hides critical gaps like doses given too early or too late. Vaccination #timeliness -- receiving doses within the optimal, age-appropriate window -- is not as well tracked.

Timeliness is important everywhere, but may be particularly important in places with relatively high coverage, to make sure that children are protected by vaccines before they are exposed to vaccine-preventable diseases.

Timeliness is currently underexamined due to inconsistent definitions, poor data quality (like missing birth dates), and a lack of fine-scale estimates to track how timeliness varies within countries.