The impact of ‘bad’ science on judicial decision-making is a thorny aspect of the relationship between science and law. This study employs doctrinal and empirical analysis to explore two Italian judgments that asserted a causal link between childhood vaccines and autism. Using a combination of actor–network theory and legal pragmatism, we uncovered a network of actors and institutions internal and external to the legal system enabling these impactful decisions that went on to contribute to a crisis in vaccination coverage in Italy. These include trial strategies, resources, communication practices between arms of government, awareness and responsiveness of institutional actors, and institutional mechanisms governing the integration of scientific expertise into the legal process. By forensically analysing how a ‘zombie idea’ received a patent of legitimacy in the Italian context, this study provides useful lessons for legal systems grappling with complex and contested public health matters.