Measuring Zero-Dose Children: Reflections on Age Cohort Flexibilities for Targeted Immunization Surveys at the Local...

Area of Science:

• Global Health
• Immunization Programs
• Public Health Surveillance

Background:

• Zero-dose (ZD) children are a key global health objective, central to the Immunization Agenda 2030 (IA2030).
• Diphtheria-tetanus-pertussis (DTP1) vaccine coverage is the standard indicator for ZD children, typically assessed via caregiver reports for children aged 12-23 months.
• Country-level needs may necessitate alternative ZD measurement strategies beyond the global definition.

Purpose of the Study:

• To discuss flexible age cohort inclusion in targeted surveys for ZD measurement.
• To explore how different age cohorts inform immunization timeliness, catch-up activities, and programmatic priorities.
• To enhance the utility of ZD data for rapid learning cycles and decision-making.

Main Methods:

• Summarized discussions from the Zero-Dose Learning Hub (ZDLH) initiative, involving multiple organizations across four countries.
• Considered practical aspects of age cohort selection, including sample size, recall bias, and data relevance.
• Evaluated the benefits of including the first year of life cohort in surveys.

Main Results:

• The ZDLH initiative recommended including the age cohort from 18 weeks to 23 months.
• This approach allows for disaggregation of results across two cohort years, aiding in identifying systematically missed communities.
• Flexibility in age cohort selection for local surveys is proposed as a key principle.

Conclusions:

• Including the first year of life cohort in surveys improves data utility for current program targets and rapid learning.
• Further research is needed to understand how improved DTP1 timeliness in the first year correlates with ZD outcomes in the 12-23 month cohort.
• Flexible age cohort inclusion in targeted surveys is crucial for effective local-level ZD measurement and program improvement.