Moderna stock tumbles after leaked melanoma vaccine data, even as full results show a 42% risk reduction

Moderna’s personalized cancer vaccine delivered the kind of late-stage trial result many investors had been waiting for, and the stock fell anyway. Shares dropped as much as 25% on Thursday, Oct. 22, after partial data from the Phase 3 melanoma trial leaked, CNBC reported, and closed more than 17% lower, according to Reuters.

This article is for general information only and is not financial or medical advice.

Why did Moderna stock drop?

The short answer from analysts: expectations. Moderna shares had nearly quadrupled since August, when Moderna and partner Merck announced that the trial had succeeded without releasing the actual numbers, Reuters reported. CNBC put the stock’s gain this year at more than 530% as of Thursday afternoon.

Several Wall Street analysts had said before the release that investors were looking for the combination to cut the risk of recurrence by 40% or more, according to Reuters. The data landed right around that bar, and the leak on an oncology website came before the companies’ full release later in the day.

Analysts were divided on what the reaction meant:

• BMO Capital Markets analyst Evan Seigerman called the result “clinically meaningful” and said the selloff “likely reflects inflated expectations into the full data release, rather than a true indictment on the efficacy of the combo therapy,” per CNBC.
• UBS analysts called it “overall a strong data set,” CNBC reported.
• RBC analyst Trung Huynh was more cautious: “This data makes us less optimistic as melanoma was supposed to be the best case,” he wrote, according to Reuters.

Merck shares fell too, by about 1% according to CNBC and about 1.8% at the close according to Reuters.

What did the Moderna and Merck cancer vaccine trial show?

The vaccine, called intismeran autogene, is built from mutations unique to each patient’s tumor and is given alongside Merck’s immunotherapy Keytruda. In the Phase 3 trial of more than 1,100 patients, the companies reported:

• A 42% reduction in the risk of melanoma recurrence or death versus Keytruda alone.
• A 38% reduction in the risk of the cancer spreading to distant parts of the body, or death.
• About 82% of patients on the combination were alive without their melanoma returning at two years, versus 70% on Keytruda alone.

CNBC reported that a separate analysis after the six-month vaccine regimen showed a 58% reduction in risk of recurrence or death. The companies said it’s still too early to know whether the treatment helps patients live longer overall.

“This is highly statistically significant. It is not by chance,” trial investigator Dr. Hussein Tawbi of the University of Texas MD Anderson Cancer Center told Reuters. He told CNBC the vaccine’s added benefit comes with much milder side effects, such as injection-site pain, than other cancer treatments.

Detailed results are set to be presented at the European Society for Medical Oncology meeting in Madrid this weekend.

How does an mRNA cancer vaccine work?

Keytruda removes a natural brake that cancer cells use to hide from the immune system, while the mRNA vaccine instructs the patient’s cells to produce copies of tumor-specific mutations so the immune system can seek them out and destroy them, Reuters explained. Because each shot is personalized, manufacturing can take about six weeks, CNBC reported, though Merck believes it can shorten that.

What’s next for Moderna?

Moderna CEO Stéphane Bancel told Reuters the companies are preparing to file for US approval and expect a launch in 2027. The combination is also being tested in kidney, bladder and lung cancers. Bancel said he believes the vaccine should add to efficacy “everywhere that Keytruda works,” though how much remains to be seen.

Merck’s research chief, Dr. Dean Li, urged patience. “I can dream of creating a log cabin, but we got some wood chops, and we’ve just knocked down one tree,” he told CNBC. “Knocking one tree does not give you a cabin or a village.”

For Moderna, a cancer product could add a major new line beyond its COVID-19, flu and RSV vaccines, CNBC noted.

FAQ

Is the Moderna cancer vaccine approved? Not yet. The companies are preparing to seek US approval and expect a 2027 launch, according to Reuters.

How much did Moderna stock fall? It fell as much as 25% during trading and closed down more than 17% on Oct. 22.

What cancer is the Merck-Moderna vaccine for? This trial was in melanoma patients after surgery; other trials cover lung, bladder and kidney cancer.