Effective Coverage in Health Systems: Evolution of a Concept.

The manner in which high-impact, life-saving health interventions reach populations in need is a critical dimension of health system performance. Intervention coverage has been a standard metric for such performance. To better understand and address the decay of intervention effectiveness in real-world health systems, the more complex measure of "effective coverage" is required, which includes the health gain the health system could potentially deliver. We have carried out a narrative review to trace the origins, timeline, and evolution of the concept of effective coverage metrics to illuminate potential improvements in coherence, terminology, application, and visualizations, based on which a combination of approaches appears to have the most influence on policy and practice. We found that the World Health Organization first proposed the concept over 45 years ago. It became increasingly popular with the further development of theoretical underpinnings, and after the introduction of quantification and visualization tools. The approach has been applied in low- and middle-income countries, mainly for HIV/AIDS, TB, malaria, child health interventions, and more recently for non-communicable diseases, particularly diabetes and hypertension. Nevertheless, despite decades of application of effective coverage concepts, there is considerable variability in the terminology used and the choices of effectiveness decay steps included in the measures. Results frequently illustrate a profound loss of service effectiveness due to health system factors. However, policy and practice rarely address these factors, and instead favour narrowly targeted technical interventions.