Objectives A National immunization Technical Advisory Groups (NITAG) is a body of national experts that empowers and provides guidance to national health policy makers to enable them to make evidence-based decisions on immunisation. The aim of this study was 1) To develop a framework for the assessment of NITAGs that will allow to understand how closely their operations are aligned with best practice; 2) to investigate whether differences with best practice are influenced by economic or geographic differences between countries; and 3) to understand the impact of NITAG alignment on the adoption of vaccines in the country’s national immunisation programme. Methods Building on previous initiatives mostly undertaken by the World Health Organization, we conducted interviews and in-depth research on 35 NITAGs worldwide and built an assessment framework with 48 indicators to evaluate NITAG Alignment with international guidance. Results The assessment revealed that there is a high variability in the degree of NITAG Alignment between countries which could not be explained by differences in GDP per capita, health expenditure per capita, or geographic location. Countries with a reasonably well-aligned NITAG have a higher proportion of the WHO-recommended and additional vaccines in their national immunization programme. Some lower and middle income countries with fairly strong alignment scores for recently established NITAGs have basic immunisation programmes. This study also found that NITAGs are usually developed following a stepwise maturing process. Conclusions Our detailed analysis of data from 35 countries suggests that, with the right support, all countries – regardless of their GDP/capita, health expenditures and geographical location – have the potential to establish highly performing NITAGs that are well-aligned with international recommendations. Well-aligned NITAGs are generally instrumental for having strong immunisation programmes. Through awareness of its position in this maturation process, a NITAG can focus on the appropriate next step for development and strengthening.