Moderna and Merck Shares Decline Following Potential Melanoma Vaccine Data Leak

On October 22, 2026, shares of Moderna (MRNA) and Merck declined due to reports of a potential data leak concerning their experimental melanoma vaccine. The companies are set to present full Phase 3 trial data at a medical conference in Madrid, and the leak has caused investor concern ahead of the anticipated official results. The vaccine, which employs mRNA technology, is being tested in conjunction with Merck's Keytruda.