PreVenTB Trial: A Critical Appraisal

Why It Matters

Accurate assessment of TB vaccine efficacy is essential for global health strategies and funding decisions; mis‑interpretation could mislead policymakers and divert resources from more effective interventions.

Key Takeaways

• PP analysis prioritized over mITT, increasing bias risk
• Neither VPM1002 nor Immuvac showed significant efficacy on primary endpoint
• Secondary extrapulmonary TB results lack clear biological justification
• Overstating exploratory findings could mislead policymakers and funders
• Transparent reporting of all trial outcomes essential for TB vaccine development

Pulse Analysis

Tuberculosis remains the world’s deadliest infectious disease, responsible for over 1.5 million deaths annually, and the search for an effective adult vaccine is a top priority for the WHO. The PreVenTB trial, a large phase 3 study conducted among household contacts in India, evaluated two candidates—VPM1002, a recombinant BCG strain, and Immuvac, a Mycobacterium‑w‑based formulation—against a placebo. While the trial’s scale and rigorous double‑blind design were commendable, the broader public‑health community is watching closely for clear efficacy signals that could justify massive rollout and funding.

The WHO advisory group’s critique centers on methodological choices that could skew efficacy estimates. The trial’s protocol identified a modified intention‑to‑treat (mITT) analysis as primary because it preserves randomisation and minimizes bias from post‑randomisation exclusions. Instead, the authors highlighted per‑protocol (PP) results, which omitted participants who missed the second dose—a placebo in this study—thereby inflating apparent vaccine performance. Moreover, the primary composite endpoint (pulmonary + extrapulmonary TB) showed no statistically robust protection for either vaccine, yet secondary analyses of extrapulmonary disease and age‑based subgroups were emphasized without a solid biological rationale. Such emphasis risks overstating benefits that may not translate into real‑world impact, especially since pulmonary TB drives transmission.

For policymakers, funders, and researchers, the lesson is clear: transparent, full‑spectrum reporting is non‑negotiable. Over‑reliance on exploratory findings can misguide allocation of billions of dollars earmarked for TB control and vaccine development. The WHO’s call for caution underscores the need for future trials to pre‑specify clinically meaningful endpoints, adhere to the intended primary analysis, and publish all results—positive or negative—to accelerate the discovery of truly protective TB vaccines and inform evidence‑based public‑health strategies.