Incorporating efficacy data from initial trials into subsequent evaluations: Application to vaccines against respiratory syncytial virus.

Background: When a randomized controlled trial fails to demonstrate statistically significant efficacy against the primary endpoint, a potentially costly new trial would need to be conducted to receive licensure. Incorporating data from previous trials might allow for the conduct of more efficient follow-up trials to demonstrate efficacy, speeding the availability of effective vaccines.
Methods: Based on the outcomes from a failed trial of a maternal vaccine against respiratory syncytial virus (RSV), we simulated data for a new Bayesian group-sequential trial. The data were analyzed either ignoring data from the previous trial (i.e., weakly informative prior distributions) or using prior distributions that incorporate the historical data into the analysis. We evaluated scenarios where the efficacy in the new trial was the same, greater than, or less than the efficacy in the original trial. For each scenario, we evaluated the statistical power and type I error rate for estimating the vaccine effect following interim analyses.
Results: If a stringent threshold is used to control the type I error rate, the analyses that incorporated historical data had a small advantage over trials that did not. If control of type I error is less important (e.g., in a post-licensure evaluation), the incorporation of historical data can provide a substantial boost in efficiency.
Conclusions: Due to the need to control the type I error rate in trials used to license a vaccine, the incorporation of historical data provides little additional benefit in terms of stopping the trial early. However, these statistical approaches could be promising in evaluations that use real-world evidence following licensure.
Competing Interests: Conflicts of Interest. DMW has received consulting fees from Pfizer, Merck, GSK, and Affinivax for work unrelated to this manuscript, and research grants from Pfizer and Merck for work unrelated to this manuscript. JLW has received consulting fees from Pfizer for work unrelated to this manuscript. VEP is a member of the WHO Immunization and Vaccine-related Implementation Research Advisory Committee (IVIR-AC). The other authors declare no conflicts.