Term	Definitions5	Example
Up-to-date coverage	Up-to-date immunization coverage refers to assessing coverage in a specific age-cohort in relation to how many doses of vaccine have been received by a particular milestone age. The number of doses is informed by NACI recommendations and the relevant P/T immunization schedule.	≥ 4 doses of pertussis-containing vaccine by the 2nd birthday (numerator definition)
On-time coverage	On-time immunization coverage refers to the proportion of children in a particular age cohort who have received all valid doses required to be on-time and up-to-date by specific milestone ages (typically by the first or second birthday). The assessment is made examining doses for multiple vaccine series, as per the routine schedule. Thus, even if one dose of a particular antigen is late, the child will not be considered on-time. In practice, a leeway period is often used for calculating on-time coverage (i.e., a 1 month leeway period after the recommended date for vaccine administration).	All doses for all recommended vaccines (as per the P/T schedule) administered within 1 month of recommended interval by the 2nd birthday (numerator definition)
Minimum interval	The minimum interval of time recommended between 2 vaccine doses to allow for the body to mount an appropriate immune response before the subsequent dose is received. Minimum intervals are typically shorter than the recommended spacing of vaccines outlined within routine immunization schedules. Minimum intervals are informed by NACI or other (e.g., ACIP) expert body recommendations.	1 month (defined as 28 days) between doses of live virus vaccines
Valid/invalid dose	A valid dose is one that is delivered in accordance with decision support rules outlining the minimum age recommended for vaccine administration and/or the minimum time interval between 2 doses of vaccine. Doses that are administered too early (before the minimum age and/or before the minimum interval has elapsed) are considered invalid and are not typically ‘counted’ in the dose assessment used for coverage assessment.	A child who receives MMR vaccine at 12 months of age and again 14 d later would be regarded to have received only 1 valid dose of MMR. The second dose was administered before the minimum interval and is considered invalid.
Grace period	When used, grace periods provide an allowable period before dose eligibility such that an administered dose can still be considered valid.	If a 4 day grace period is used, doses of MMR administered up to 4 d before a client turns 1 y of age, would be considered valid doses for the purposes of coverage assessment (assuming 12 months of age is used as the minimum age)

Note: To generate a coverage estimate, the numerator (of children with the requisite number of valid doses) is divided by the eligible population (denominator). For coverage assessment, the numerator is divided by the denominator, which CIRC defines as all children within a defined birth cohort who are current residents in the P/T during the time period of interest (not only those who present for immunization).⁵