CAMBRIDGE, Massachusetts — Moderna and Merck on Sunday presented full Phase 3 data for their personalised melanoma vaccine, showing that mRNA-4157 combined with Keytruda reduced the risk of recurrence or death by 42% versus Keytruda alone.

The companies' individualised neoantigen therapy trains the immune system to attack mutations unique to each patient's tumour. The data follow an 18% share drop last week, suggesting investors remained cautious despite the positive headline result.

The therapy sustained its benefit in high-risk stage III and IV melanoma patients, with a distant metastasis-free survival advantage that the companies said supports a regulatory filing. Moderna's chief medical officer, Paul Burton, previously described the programme as potentially approvable by 2027, pending accelerated review.

Analysts at Jefferies and Bank of America have questioned whether the complex manufacturing required for bespoke vaccines can scale commercially—a concern cited as a factor in the stock's recent decline. Moderna said it was expanding its individualised-therapy production capacity to address those doubts.

Merck and Moderna are running parallel trials applying the same platform to lung, kidney and bladder cancers, positioning the melanoma result as a proof point for a broader oncology pipeline.