Moderna Stock Explodes 177% on Cancer Vaccine Breakthrough

Moderna closed at $174.38 on 19 August 2026, up $111.42 from the previous close of $62.96. That is a gain of 176.97% in a single session. The cover page of the company's Form 10-Q for the quarter ended 30 June 2026 reports 399,235,889 shares of common stock outstanding as of 24 July, which puts the increase in market value at about $44.5bn and the company itself at roughly $69.6bn, up from about $25.1bn the day before.

Merck moved with it, closing at $152.20, up 12.60% from $135.17. On roughly 2.47 billion shares outstanding that is about $42bn of market value added, so the two companies together gained roughly $86bn between one close and the next. Nothing was approved, nothing was sold and nothing was filed with the regulator that day. The entire repricing rests on a single document.

That document was a joint press release issued that morning by Merck and Moderna. The Phase 3 INTerpath-001 trial, registered as NCT05933577, met its primary endpoint of recurrence-free survival and its key secondary endpoint of distant metastasis-free survival. The trial enrolled 1,137 patients with completely resected stage IIB, IIC, III or IV cutaneous melanoma and randomised them 2:1 to intismeran autogene plus Keytruda or to Keytruda alone, for approximately one year.

What the announcement does not contain

The release says that at a pre-specified interim analysis the combination demonstrated statistically significant and clinically meaningful improvements in recurrence-free survival and distant metastasis-free survival compared to Keytruda alone. It gives no hazard ratio for INTerpath-001. It gives no p-value, no confidence interval, no median follow-up, no event counts and no recurrence numbers for either arm. Overall survival is described as still being evaluated. On safety it says the profiles were consistent with previously reported studies with no new signals observed, and provides no adverse event rates for this trial.

The two hazard ratios that do appear in the release come from a different study. KEYNOTE-942 was a Phase 2b trial that enrolled 157 patients between July 2019 and September 2021, 107 on the combination and 50 on pembrolizumab alone, and was published in The Lancet. Its five-year figures, presented at the 2026 ASCO annual meeting, are a 49% reduction in the risk of recurrence or death, hazard ratio 0.51 with a 95% confidence interval of 0.294 to 0.887, and a 59% reduction in the risk of distant metastasis or death, hazard ratio 0.411 with an interval of 0.200 to 0.843. The upper bound on the recurrence-free survival interval sits close to 1. Both companies say the Phase 3 results will be presented at a future medical meeting.

Both halves of the partnership repriced

Moderna does not own the drug on its own. Note 5 to the second-quarter 10-Q sets out the arrangement. Merck exercised its option on the individualised neoantigen therapy in September 2022 and paid Moderna a $250 million option exercise fee in October 2022. Since then, in the filing's words, costs and any profits or losses are generally shared equally on a worldwide basis. Moderna is primarily responsible for process development and manufacture of the material, Merck generally leads the clinical trials, and the collaboration is accounted for under ASC 808.

Moderna's $44.5bn and Merck's $42bn are therefore two valuations of the same half-owned asset, and they sit within about 6% of each other. The difference in percentage terms, 176.97% against 12.60%, is a function of where the two companies started rather than of how the drug is owned. Merck is a far larger company and sells Keytruda at scale today, while Moderna was worth about $25.1bn and sells very little.

Against the size of the company

What Moderna spends on the programme is disclosed. For the six months to 30 June 2026 it recognised $198 million of expense on the neoantigen collaboration, net of Merck's reimbursements, compared with $203 million in the same period of 2025. Total Moderna revenue in the first half of 2026 was $534 million and the net loss was $2,125 million. Shareholders' equity at 30 June stood at $6,761 million. The one-day increase in market value was about 6.6 times the company's entire book value and roughly 225 times its half-year net spending on the programme that produced it.

The readout was not itself a surprise, only its timing. The 10-Q filed on 31 July told shareholders that the Phase 3 adjuvant melanoma study was fully enrolled and that data were expected potentially in 2026. Nine Phase 2 and Phase 3 trials of intismeran are under way across melanoma, non-small cell lung cancer, bladder cancer and renal cell carcinoma.

The sector move

The rest of biotech was carried along. The Nasdaq Biotechnology Index closed at 7,404.92, up 444.59 points or 6.39%. That number is specific to that index and does not carry across. The SPDR S&P Biotech ETF rose 5.90% to $169.55 and the iShares Biotechnology ETF rose 6.58% to $216.96 on the same day. The S&P 500 rose 0.21% and the Nasdaq Composite 0.16%, so this was one drug rather than a general change in appetite for risk.

As of the close on 19 August, Moderna had not filed a Form 8-K on the results. Disclosure by broadly disseminated press release satisfies Regulation FD, so nothing is missing from the filing record. What is missing is the effect size. An independent monitoring committee has seen the numbers and the two companies have chosen to hold them for a conference. Until that presentation, about $86bn of combined market value added on one day rests on the phrase statistically significant and clinically meaningful, and on a hazard ratio drawn from a trial roughly one seventh the size of the one being announced.