It is commonly argued that the decision to introduce a new vaccine is properly based on objective and measurable criteria, including disease burden and efficacy of the vaccine. Moreover, new vaccines are to be introduced rapidly and globally: delay is difficult to justify. Historical studies of new vaccine introductions paint a rather different and more complex picture. The few studies comparing new vaccine introduction in different countries suggest that ‘evidence’ for the efficacy of a vaccine was commonly subjected to varying interpretations. This paper, based on analysis of the introduction of the measles–mumps–rubella (MMR) vaccine in Denmark and the Netherlands, takes this argument further. Though both countries are – and were – small welfare states with well-organised national immunisation programmes, both adopted MMR a full decade after its introduction in the USA. The paper suggests that the reasons for delaying, in each case, are a reasonable reflection of each country’s concerns, perceptions of the three diseases, and technological approaches already adopted. There were differences in each of these respects. The decision to adopt MMR, which each country eventually took, was significantly influenced by the political and ideological changes taking place in the 1980s, including a growing emphasis on costs and benefits, as well as the growing influence of the international context.