Moderna is up 600% on a cancer vaccine. Its partner Merck hasn't moved.

Moderna's revenue fell from $18 billion a year to $145 million a quarter.
The stock is up more than 600% this year.
The company that owns half of the reason has not moved.

The reason is a cancer vaccine. On September 21 Moderna and Merck reported that intismeran, a personalised vaccine for melanoma, met its endpoints in a Phase 3 trial. Moderna rose 12% that day and 39 points against the S&P since, to a 52-week high on Friday.

The part the tape skipped: the vaccine is not Moderna's alone. Merck co-develops it and makes Keytruda, the drug it is paired with. If intismeran works, it extends the life of the biggest cancer drug in the world. Since the result Merck is down 1%.

Clargus asked what Moderna is connected to in the last 30 days: one molecule, one partner, and one downgrade.

The downgrade: Citi cut Moderna to Sell on valuation in early October, with analysts putting intismeran's eventual sales at up to $5 billion a year. On $145 million of quarterly revenue and an $800 million quarterly loss, a shared $5 billion drug is most of the market value. For Merck it is a rounding error on Keytruda.

My read: the market has priced the vaccine entirely in the small company and not at all in the large one. Scale explains some of that, not all of it.

What proves this wrong: ESMO data narrower than the headline, or a regulatory path longer than the stock assumes. Then Moderna gives back the move and Merck never had it.

One drug, two tapes. Only one of them can be right about what it is worth.