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Moderna melanoma vaccine data surface early; shares fall 17.6%

The Phase 3 INTerpath-001 results were positive, but the 42% reduction came in below the 49% seen in the earlier Phase 2b study, though the trials are not directly comparable. Full data are due at ESMO in Madrid on 24 October.

By Rowan Ashby Published 22.10.26 20:16 UTC 6 min read

Exterior of Moderna's headquarters building in Cambridge, Massachusetts — ajay_suresh / Wikimedia Commons / CC BY 4.0 · Source

Key takeaways

Moderna shares closed 17.6% lower at $202.63 on 22 October 2026, after falling as much as 26% intraday. Merck closed 1.8% lower at $147.25 (Yahoo Finance data, as of 20:00 UTC).
The selloff began after Phase 3 INTerpath-001 results for the melanoma vaccine intismeran autogene appeared early online, two days before their scheduled ESMO presentation, according to Bloomberg and Investing.com.
Merck later released the data. Intismeran plus Keytruda cut the risk of recurrence or death by 42% (hazard ratio 0.58) and the risk of distant metastasis or death by 38% (HR 0.62), compared with Keytruda alone.
The Phase 3 headline number came in below the 49% reduction from the earlier Phase 2b study, though the two trials are not directly comparable. Overall survival data are not yet mature.
Full data will be presented at the ESMO Congress Presidential Symposium in Madrid on Saturday, 24 October, at 10:30 a.m. EDT.

Why Moderna melanoma vaccine data hit the shares

Moderna shares closed 17.6% lower at $202.63 on Thursday after Moderna melanoma vaccine data appeared online two days before their ESMO presentation. The Phase 3 results were positive. Merck, its partner on intismeran autogene, closed 1.8% lower at $147.25.

The figures were first shared on social media. According to Bloomberg, details began circulating on X from unverified sources, and one account cited a report attributed to the medical news site Oncology Central. Investing.com reported that the report appeared on that site at about 12:30 p.m. ET and was taken down soon after. Bloomberg described it as a "possible leak" of data that was meant to be released this weekend.

At 2:59 p.m. EDT, Merck published the detailed results in a news release. It said the data had been chosen for an official ESMO press briefing and accepted for publication in The New England Journal of Medicine.

How Moderna and Merck shares moved

Stock	Previous close (21 Oct)	Close (22 Oct)	Change	Intraday low
Moderna (MRNA)	$245.81	$202.63	-17.6%	$180.80 (-26.4%)
Merck (MRK)	$149.88	$147.25	-1.8%	$144.07 (-3.9%)

Source: Yahoo Finance chart data, regular session close, data as of 22 October 2026, 20:00 UTC.

Before the slide, Moderna shares had risen in the days leading up to the data. Yahoo Finance data show the stock closed at $218.01 on 16 October and $245.81 on 21 October, a gain of about 12.8% in four sessions. At its low of $180.80, the stock was down 26.4% from the previous close.

What the Phase 3 INTerpath-001 numbers say

INTerpath-001 is a randomised, double-blind Phase 3 trial. It enrolled 1,137 patients with stage IIB to IV melanoma whose tumours had been fully removed by surgery. Patients were assigned 2:1 to intismeran plus Keytruda (pembrolizumab) or to placebo plus Keytruda. Median follow-up was 24.6 months, according to Merck.

Measure	Intismeran + Keytruda	Keytruda alone	Hazard ratio (95% CI)
Recurrence-free survival at 2 years	82.2%	70.0%	0.58 (0.45–0.75)
Distant metastasis-free survival at 2 years	88.5%	80.2%	0.62 (0.45–0.85)
Grade 3–5 treatment-related adverse events	14.2%	13.4%	n/a

Source: Merck news release, 22 October 2026.

The release also reported a time-based pattern. In the first six months, the hazard ratio for recurrence-free survival was 0.99, which means no difference between the two arms. After six months, a pre-specified sensitivity analysis gave a hazard ratio of 0.42, a 58% reduction in risk. A modified analysis that counted only patients who received at least one planned dose showed a 49% reduction.

Merck said overall survival data are not yet mature, though it reported a favourable trend. The company said there were no new safety signals. The most common side effects in the combination arm were fever, injection-site pain and fatigue.

What the companies disclosed in August

The two companies first said on 19 August that INTerpath-001 had met its primary endpoint of recurrence-free survival and its key secondary endpoint of distant metastasis-free survival. They gave no numbers at the time. According to the August release, the results came from a pre-specified interim analysis. BioPharma Dive reported then that Moderna's market value rose by about $45 billion in one session.

The same release restated the five-year results of the earlier Phase 2b KEYNOTE-942 study: a 49% cut in the risk of recurrence or death (HR 0.51) and a 59% cut in the risk of distant metastasis or death (HR 0.411). Bloomberg noted that the earlier study had a different patient group and a different follow-up period, so the figures are not a direct comparison.

Why the shares fell despite a positive readout

No company has given an official explanation for the move. Published reporting points to several factors.

Expectations. Reuters reported that several Wall Street analysts said before the meeting that investors wanted at least a 40% cut in recurrence risk. The 42% result cleared that bar, but only narrowly, and it was below the 49% from the Phase 2b study. In August, BioPharma Dive quoted Evercore ISI analysts who said a reduction of 35% to 40% would be "clearly differentiated".
Valuation. In August, Evercore ISI's Cory Kasimov said Moderna's valuation already priced in "substantially more conviction" than the data disclosed at the time supported, according to BioPharma Dive.
The early release. Investors received partial figures through an unverified source in the middle of the trading day, before the companies' full release and before any context from the investigators. Moderna, Merck and ESMO did not immediately respond to Bloomberg's requests for comment. How the report came to be published early has not been confirmed.

Moderna's sensitivity to this single programme is much greater than Merck's. Keytruda is already one of the world's best-selling medicines, according to Reuters, and Merck is a far larger and more diversified company.

What it means

From a clinical point of view, the trial is a landmark. Reuters reported that it is the first trial to show that this kind of combination can keep melanoma at bay. Merck research chief Dean Li said INTerpath-001 is "the first Phase 3 study to demonstrate a clinically meaningful improvement" in both recurrence-free and distant metastasis-free survival. The companies say they are in talks with regulators based on the data.

For the market, the question is what the vaccine could be worth commercially, not whether it works. Investors are likely to focus on the flat first six months, the size of the benefit after that, the lack of overall survival data so far, and per-patient manufacturing costs. Leerink's Daina Graybosch raised the cost issue in August, according to BioPharma Dive.

The selloff also shows how biotech stocks that have rallied ahead of a known event can fall even on good news.

What to watch at ESMO and next

24 October, 10:30 a.m. EDT: Georgina Long presents the full INTerpath-001 results (LBA1) at the ESMO Presidential Symposium in Madrid, according to Moderna.
24 October, 1:00 p.m. EDT: Moderna investor webcast.
25–26 October: ESMO posters on intismeran in pancreatic cancer and in early-stage lung cancer (INTerpath-014).
29 October: Merck third-quarter results.
Later: regulatory filings, the NEJM paper, and mature overall survival data. No filing timeline has been announced.

Readers may also want our US stocks daily brief for 21 October, coverage of the chip stock slump, Tesla's third-quarter results, and Netflix's margin guidance.

Frequently asked questions

Why did Moderna stock fall on 22 October 2026?

Moderna shares closed 17.6% lower after Phase 3 INTerpath-001 results for its melanoma vaccine appeared online before their scheduled ESMO presentation. The result, a 42% cut in recurrence risk, was positive. However, it was below the 49% seen in the earlier Phase 2b study, and investors had high expectations. No official reason for the move has been given.

What did the INTerpath-001 trial show?

According to Merck, adding intismeran autogene to Keytruda cut the risk of melanoma recurrence or death by 42% (hazard ratio 0.58) and the risk of distant metastasis or death by 38% (HR 0.62) compared with Keytruda alone, in 1,137 patients with resected stage IIB-IV melanoma. Overall survival data are not yet mature.

When will the full intismeran data be presented?

The full results will be presented at the ESMO Congress Presidential Symposium in Madrid on Saturday, 24 October 2026, at 4:30 p.m. CEST (10:30 a.m. EDT). Moderna will hold an investor webcast at 1:00 p.m. EDT the same day.

Is the Moderna-Merck melanoma vaccine approved?

No. Intismeran autogene is still an investigational therapy. The companies say they are in talks with regulators based on the Phase 3 data, but no filing timeline has been announced.