Success is only half the story—understanding why success happens is where real transformation begins. In global health, especially in immunisation, results alone can mislead. Imagine launching an outreach programme in a remote village: six months later, vaccination rates finally rise. Celebration seems in order—but pause for a moment. Do we know why it worked?
Was it the village elders’ advocacy that boosted trust? Did parents grow more confident about side effect safety? Or did steady vaccine deliveries quietly make the biggest difference? Without understanding these dynamics, replicating—or even sustaining—success becomes a guessing game.
To reach the millions of zero-dose and under-immunised children worldwide, it’s not enough to ask, Did the programme work? The vital question is, Why did it work—or not? This is where traditional monitoring often falls short. Standard evaluations can prove effectiveness, but they rarely uncover the hidden mechanisms—the social, behavioural, and contextual “black box” that explains change. And this missing piece can mean the difference between a programme that scales sustainably and one that flatlines after early wins.
Opening the black box with theory-based evaluation
Theory-based evaluation challenges that status quo. It ensures that every data point, activity, and decision aligns with a logical model—a clear pathway that explains how and why impact should occur. Instead of assuming that a successful outcome will magically repeat, this method digs deeper to uncover causal links between actions and results.
It maps not only what a programme does but the reasoning behind it. Was awareness-raising the key trigger? Did increased trust pull hesitant parents closer to health services? By grounding evaluation in theory, practitioners can test assumptions instead of relying on anecdotes or luck.
This clarity becomes even more urgent for zero-dose children, who often live in conflict zones, migrate frequently, or face deep-rooted social fear around vaccines. In these environments, a theory-based approach reveals why certain strategies thrive while others falter—equipping implementers to adjust and policymakers to scale proven interventions confidently.
Lessons from Uganda: when evaluation becomes design
Take Uganda’s experience. When the Uganda Learning Hub set out to evaluate a project engaging community leaders in promoting vaccination, the team soon realised something crucial: the initiative lacked a clear explanation of how those leaders were expected to influence caregivers. Were they spreading awareness? Dispelling myths? Providing transportation or incentives?
By working with implementers to unpack these questions, the evaluation process itself evolved into a tool for programme improvement. Once pathways were clarified, messages became sharper, activities more focused, and progress easier to track.
And here’s the real takeaway—theory-based evaluation doesn’t just measure success; it actively creates it. It empowers implementers to refine their strategies in real time, turning learning into performance.
The power of a theory of change
At the heart of this approach lies the theory of change: a structured framework connecting programme activities to their intended outcomes and the assumptions underpinning each step. Think of it as a roadmap that makes every hypothesis visible so it can be tested and improved.
Unlike traditional logframes that document what will be done, a theory of change asks why those actions should work and how progress actually unfolds. This makes it invaluable in volatile environments where flexibility can determine success.
Collaboration strengthens every theory
Across the Learning Hubs, collaboration proved essential in shaping meaningful theories of change. In Mali, for instance, government agencies, district health officers, civil society groups, and partners sat together to co-design the logic behind their immunisation efforts. They aligned innovative tools like digital supervision systems with existing national strategies, creating consensus on how change was expected to occur.
This joint ownership turned a static theory of change into a living guide—one that stakeholders continually revisited and refined. It wasn’t just a report—it became a shared compass for decision-making.
Keeping theories alive: lessons from Bangladesh
Too many programmes treat the theory of change as a one-time exercise. But reality rarely stands still. In 2024, Bangladesh experienced political turmoil that disrupted field operations. The Learning Hub team responded by updating assumptions within their theory of change, enabling quick programme adjustments to minimise setbacks.
For example, lockdowns and local violence upended original outreach strategies. By revising their change model collaboratively with government counterparts, the team adapted in real time and maintained progress toward immunising hard-to-reach children. The lesson? A theory of change must evolve alongside the world it seeks to improve.
Inside the toolkit: practical questions that matter
The Zero-Dose Learning Hub Toolkit – Designing and Evaluating Zero-Dose Programs with Theory-Based Approaches (available at https://zdlh.gavi.org/resources/designing-and-evaluating-zero-dose-programs-theory-based-approaches-toolkit) distils all these lessons into actionable guidance. It helps programme teams move beyond surface-level evaluation to ask deeper, smarter questions:
- How exactly did improvements in coverage occur?
- Which original assumptions held up, and which didn’t?
- How did context—political unrest, social barriers, supply chain issues—shape results?
- Were there unexpected consequences, good or bad, that should influence future planning?
The toolkit includes examples from Learning Hubs in Bangladesh, Mali, Nigeria, and Uganda, providing adaptable templates for a wide range of settings.
From ‘Did it work?’ to ‘Why did it work?’
The new frontier in global immunisation isn’t just proving effectiveness—it’s understanding causality. By focusing on the “why,” theory-based frameworks help identify the drivers of meaningful, lasting change. They guide smarter design, stronger evidence, and quicker adaptation when contexts shift.
The Designing and Evaluating Zero-Dose Programs with Theory-Based Approaches Toolkit is now live at https://zdlh.gavi.org/. Explore it today and see how theory-based methods can fortify your immunisation initiatives from the inside out.
Led by JSI, in partnership with the International Institute of Health Management Research and The Geneva Learning Foundation, Gavi’s Zero-Dose Learning Hub (ZDLH) operates as a global platform to generate evidence and connect stakeholders committed to reaching every child. JSI supports Learning Hubs in Bangladesh, Mali, Nigeria, and Uganda to embed data-driven strategies under Gavi’s IRMMA framework—Identify, Reach, Monitor, Measure, and Advocate.
Through technical support, collaboration, and practical tools, these efforts aim for one shared goal: ensuring that every child, no matter where they are born, receives life-saving vaccines.
What do you think? Should evaluation be about accountability—or about learning to improve? Share your thoughts below: how can theory-based approaches reshape the way global health measures success?
