In the quest for global health, zero-dose (ZD) children stand as a critical challenge, forming the cornerstone of the Immunization Agenda 2030 (IA2030) strategy. At the heart of this strategy lies the need to measure ZD children accurately, a feat usually achieved through estimating coverage for the first dose of the diphtheria–tetanus–pertussis (DTP1)-containing vaccine.

However, a recent workshop organised by the ZD Learning Hub (ZDLH) initiative sheds light on the importance of flexibility in measuring ZD children at the local level. Engaging partners across Bangladesh, Mali, Nigeria, Uganda, and globally, the ZDLH initiative explored age cohort flexibilities, aiming to tailor measurement approaches to the diverse needs of different regions.

One of the key reflections emerging from the workshop centers on the age cohort inclusion in targeted surveys. Traditionally, DTP1 coverage estimates rely on data reported by caregivers of children aged 12–23 months. The ZDLH initiative, however, recognises that a one-size-fits-all approach might not address the unique challenges faced by communities.

The case for including other age cohorts in the first years of life becomes evident, particularly in understanding immunisation timeliness. WHO recommends administering DTP1 as early as 6 weeks of age, emphasising the importance of timely vaccination for optimal protection. By broadening the age cohort to 18 weeks to 23 months, the ZDLH initiative aims to capture early delays in DTP1, enabling insights into immunisation timeliness.

Additionally, the inclusion of multiple age cohorts in targeted surveys opens the door to valuable comparisons. Each age cohort represents a different exposure to programmatic activities, allowing for a nuanced understanding of coverage trends and drivers in communities. This approach proves beneficial in identifying systematically missed communities and adapting strategies to dynamic contexts, such as health system shocks or the introduction of new interventions.

Practical considerations also play a crucial role in this paradigm shift. While a larger sample size may be required for multiple age cohorts, the potential reduction in household visits to find eligible children offers operational efficiency. However, researchers must navigate the challenge of recall bias, especially when relying on caregiver memory for vaccination history.

The ZDLH initiative’s decision to include the age cohort from 18 weeks to 23 months stems from a careful consideration of these factors. This age range allows for the detection of delays in DTP1 and early insights into zero-dose children, aligning with the initiative’s objectives of understanding timeliness, systematically missed communities, and programmatic shifts.

Beyond the technical aspects, the ZDLH initiative emphasises the broader goal of rapid learning cycles. By including different age cohorts in the same survey, researchers aim to provide timely insights for decision-makers. This approach accelerates the timeline for measuring program impact, an essential factor in adapting strategies and addressing challenges promptly.

The ZDLH initiative’s exploration of age cohort flexibilities reflects a commitment to localised and adaptable approaches in measuring zero-dose children. By embracing the diversity of challenges faced by different communities, this initiative paves the way for more effective immunisation strategies, bringing us one step closer to achieving the goals set by the Immunization Agenda 2030. 

Reference:
Corrêa GC, Uddin MJ, Wahed T, Oliveras E, Morgan C, Kamya MR, et al. Measuring zero-dose children: Reflections on age cohort flexibilities for targeted immunization surveys at the local level. Vaccines (Basel) [Internet]. 2024 [cited 2024 Mar 7];12(2):195. Available from: https://www.mdpi.com/2076-393X/12/2/195