The question asks for a combined pentavalent 1-to-3 dropout rate across two barangays. The dropout rate measures the proportion of children who received the first dose but failed to complete the third dose. This is a core program indicator in the National Immunization Program because it reveals retention gaps that coverage alone can hide
[1][3].
Step 1 — Combine the numerators and denominators first
Pooling data before calculating is required because the two barangays contribute different numbers of children. The formula is:
Dropout rate = (Pentavalent 1 − Pentavalent 3) ÷ Pentavalent 1 × 100
Combined pentavalent 1:
140 +
100 =
240
Combined pentavalent 3:
126 +
78 =
204
Dropouts =
240 −
204 =
36
Dropout rate =
36 ÷
240 × 100 =
15.0%
Key point! The denominator is the number who received pentavalent 1, not the eligible population. Using eligible infants (
260) would incorrectly produce
13.8%, which is option 1.
Step 2 — Why not average the two barangay rates?
Barangay 1 dropout rate = (
140 −
126) ÷
140 × 100 =
10.0%
Barangay 2 dropout rate = (
100 −
78) ÷
100 × 100 =
22.0%
Simple average = (
10.0% +
22.0%) ÷ 2 =
16.0%, which is option 3.
This is incorrect because barangays have unequal cohort sizes. Barangay 1 contributes more children to the combined pool, so its lower dropout rate carries more weight. The pooled calculation automatically applies this weighting.
Watch out! Averaging percentages without considering the underlying population sizes is a common error in program monitoring. Always return to raw counts before combining rates.
Clinical and programmatic meaning
Pentavalent vaccine protects against diphtheria, pertussis, tetanus, hepatitis B, and Haemophilus influenzae type b. A child is classified as a dropout when the first dose is received but the third dose is not
[1]. High dropout indicates that children start the series but do not complete it, leaving them only partially protected.
In Tanzania, first-dose coverage was approximately
97% while third-dose coverage was only
89%, demonstrating that dropout can persist even when initial uptake is strong
[1]. Ethiopia similarly reports that individual vaccine coverage may improve while the proportion of fully vaccinated children remains low, highlighting dropout as a distinct barrier to full protection . Interventions such as text message reminders and sticker prompts have been evaluated specifically to reduce dropout, confirming that retention—not just initial access—is an actionable program target
[3].
A combined dropout rate of
15.0% means that for every
100 infants who began the pentavalent series,
15 did not receive the third dose. The nurse managing the RHU should investigate reasons for dropout—such as caregiver mobility, vaccine stockouts, or missed appointment tracking—and implement recall strategies for children who received pentavalent 1 but are overdue for pentavalent 3
[3].
| Calculation approach | Formula | Result | Interpretation |
|---|
| Pooled counts (correct) | (240 − 204) ÷ 240 × 100 | 15.0% | Weighted by actual cohort size |
| Simple average of barangay rates (incorrect) | (10.0% + 22.0%) ÷ 2 | 16.0% | Ignores unequal population sizes |
| Using eligible infants as denominator (incorrect) | (260 − 204) ÷ 260 × 100 | 21.5% | Mixes non-starters into the dropout measure |
The denominator for dropout must always be the number who received the first dose, because dropout is defined as failure to progress from dose 1 to dose 3 among those who started
[1]. Children who never received any dose are a separate access problem, not a dropout problem.
References (research sources)
- [1]
Associated factors for dropout of first versus third doses of pentavalent vaccination in Tanzania.Research articleTillya R, Abdallah G, Msuya H, Bajaria S, Mtenga S, Festo C (2025) · DOI: 10.1016/j.vaccine.2025.126962
- [3]
Reducing routine vaccination dropout rates: evaluating two interventions in three Kenyan districts, 2014.Research articleHaji A, Lowther S, Ngan'ga Z, Gura Z, Tabu C, Sandhu H (2016) · DOI: 10.1186/s12889-016-2823-5