A Shared Cancer Vaccine Passed Phase 3: Moderna +177%, Merck +12.6%

Before the U.S. market opened on August 19, Moderna and Merck said their shared cancer vaccine had hit its Phase 3 primary endpoint in resected melanoma.

By how much, they did not say: the data go to "an upcoming international medical meeting." By the close the two were worth $86 billion more, with no effect size published.

What Was Actually in the Release

INTerpath-001 covers high-risk melanoma patients whose tumors were completely resected.

Of 1,137 patients, two-thirds got Keytruda plus the vaccine and one-third Keytruda alone. The vaccine ran every three weeks up to nine doses, Keytruda every six weeks up to nine cycles, over about 56 weeks.

It reports statistically significant improvement in time to recurrence and to distant metastasis; survival data are not yet mature.

The only numerical efficacy figure is from the old 2023 Phase 2 study: a 49% cut in recurrence or death across 157 patients, on a very wide interval. The Phase 3's numbers were not published.

With No Numbers, What Did the Market Read?

A large trial is examined before it finishes by an independent committee, on a schedule written in advance. Declaring victory early is harder than declaring it at the end.

RBC's analysts noted that a readout expected at year-end arrived months early. In their words, "the strength of the underlying data must have been compelling to trigger significance." TD Cowen called it a "landmark moment," and William Blair upgraded Moderna.

A Fifty-Fifty Partnership, Two Denominators

In October 2022 Merck exercised its option for $250 million; all costs and profits are shared equally, worldwide. Moderna manufactures; Merck runs the clinical program.

Every link runs for one patient — a supply chain rebuilt per patient, not a drug off a shelf. Whether it scales is the most contested question.

If the drug is split down the middle, so is the value it creates — but that is not how it looked on a screen.

A percentage measures news against a company's size. More: What Is Market Capitalization?

Part of Merck's move blends into a health care sector that closed at a record the same day; attributing all $42 billion to the trial is an interpretation.

Why Merck Was So Pleased: The 2028 Problem

One line dominates Merck's income statement: Keytruda sold $31.7 billion in 2025, 49% of revenue, and its first patent expires in December 2028.

That does not mean it goes generic in 2029. Merck holds some thirty patent families around Keytruda; some run to 2039, and the subcutaneous formulation approved in September 2025 is protected to 2041.

Not a cliff but a slope: Bloomberg Intelligence expects sharp erosion nearer 2033 than 2029, and nobody names a firm date.

That is where the vaccine matters: intismeran is given only with Keytruda, inside a 56-week regimen. A regimen at the center of a protocol, carrying its own patents, is more than a new revenue line.

Nor is it automatic: once exclusivity lapses, a biosimilar pembrolizumab could replace branded Keytruda in the same combination.

Where the Wave Traveled

BioNTech earns nothing here, only tries the same approach in its own programs; it rose 22% anyway. What was repriced was not revenue but the odds that a method works.

The S&P 500 health care sector closed at a record, while the semiconductor index fell 1.3% and Broadcom 4%. Caught between: SPY rose 0.23% while QQQ, tracking the Nasdaq 100, slipped 0.20%.

Separately, the Treasury raised long-dated buybacks from $2 billion to at least $4 billion, and the 30-year yield backed off its highest level since 2007.

The 2025 line is the sharpest irony: this technology is the family whose funding its own government cut a year earlier. The cancellations spared oncology, but political climate discounts every branch at once.

What Is Left

Moderna's statements were untouched: $145 million of revenue and a $782 million loss in the second quarter of 2026.

It held $6.9 billion at the end of June; operations consumed $1.16 billion in the first half and a July settlement $950 million. Guidance is to end the year with $4.7 to $5.2 billion. More: What Is Cash Flow?

So the $44.5 billion handed to Moderna is roughly nine times the cash it expects at year-end — not the counterpart of revenue but the price of a probability.

On Merck's side what changed is a calendar: 2028 is still there, but the distribution of what comes after has shifted.

The second lesson is in the release: the market read not a number but a decision — an independent committee opening the trial early and calling it sufficient.

Sometimes the most informative thing is not the figure disclosed, but when it was disclosed.

This article draws on the joint Merck–Moderna release of August 19, 2026, the companies' reported financial results, and coverage from BioPharma Dive, BioSpace, TIME and Benzinga. The Phase 3 effect sizes have not yet been published; the 49% figure cited here belongs to the smaller Phase 2 study reported in 2023. Closing prices and market values come from market data providers; intraday coverage carried lower percentages because the stock continued climbing into the close. Estimates of patent duration and revenue erosion vary across institutions.

Correction (September 13, 2026): prose tightened for rhythm; figures and sources unchanged.