Situation: A nurse runs the weekly immunization session of a Barangay Health Station (BHS) under the National Immunization Program (NIP) and reviews the station's target client list. The nurse reviews last year's coverage among eligible infants: Pentavalent 1: 96% Pentavalent 3: 71% First dose of measles-containing vaccine: 68% No stock-out was recorded. What does this pattern MOST likely show?

First-dose coverage of 96% shows that families can reach and accept the service. The large fall from pentavalent 1 to pentavalent 3 (a dropout rate of about 26%) and the low coverage of the first measles-containing dose show that infants started but did not continue. This is a continuity problem: defaulters on the target client list were not identified and followed up with home visits and reminders.

Understanding the coverage pattern

The first dose of pentavalent vaccine reached 96% of eligible infants, which means families were able to access the health station and accepted the initial vaccination. The sharp decline to 71% for pentavalent 3 and 68% for the first measles-containing dose indicates that many infants started the series but did not complete it. This is a continuity problem, not an access problem.

A high first-dose coverage with a large drop in later doses defines a dropout pattern, not a failure to start vaccination. If families could not reach the station, the first-dose coverage would also be low. If the target population were overestimated, all coverage figures would be inflated, not just the first dose. True contraindications are rare and would not explain a 26% dropout between pentavalent 1 and pentavalent 3.

Immunization dropout refers to a child who received at least one dose of a multi-dose vaccine but failed to complete the recommended schedule ^[1][2]. The dropout rate is calculated by comparing the number of infants who started the schedule with the number who completed it, and it serves as a key indicator of program continuity and follow-up ^[2]. In this scenario, the dropout rate between pentavalent 1 and pentavalent 3 is approximately 26%, which is a substantial loss of children who had already engaged with the service.

Pattern	What it suggests	Why this scenario fits
High first-dose coverage, low later-dose coverage	Dropout or defaulting after starting	Pentavalent 1 at 96%, pentavalent 3 at 71%
Low coverage for all doses	Access barrier or service delivery problem	Not seen here because first dose is high
Uniformly inflated coverage	Overestimated target population	Not seen here because later doses are low
Selective non-vaccination due to contraindications	Rare and would not cause a large drop	Contraindications are uncommon and would not explain 26% dropout

Key point! The dropout rate is a direct measure of program continuity and follow-up. A high dropout rate signals that the health system is not adequately tracing children who miss subsequent doses ^[2].

The most likely explanation is that defaulters—children who received the first dose but missed later doses—were not identified and followed up. In immunization programs, active tracing through home visits, reminders, and review of the target client list is essential to reduce dropout ^[1]. Without such follow-up, children who start the series may be lost to the program, resulting in incomplete protection against vaccine-preventable diseases.

The nurse reviewing the target client list should identify children who received pentavalent 1 but not pentavalent 3 or the first measles-containing dose, then arrange for tracing and catch-up vaccination. This is the core nursing action implied by the coverage pattern. Studies in similar settings have shown that dropout is associated with factors such as lack of follow-up, poor data quality, and weak defaulter tracing mechanisms ^[1]. Monitoring dropout rates alongside coverage helps distinguish between access problems and continuity problems, guiding targeted interventions ^[2].