CAMBRIDGE, Aug. 23 -- The message that traveled fastest when Moderna and Merck reported their Phase 3 melanoma vaccine results on August 19 was not contained in a scientific paper. It was not a confidence interval or an absolute risk reduction figure. It was a stock price: Moderna's shares more than doubled in a single trading session, in a market reaction that priced years of potential ahead of a single data release the companies themselves have not yet submitted for peer review.

For patients with stage three or four melanoma waiting on the results to understand their own treatment options, the distance between that market signal and what the data actually says matters more than it does for any investor.

The vaccine, known as intismera...