Moderna Stock Plunges 25% on Cancer Vaccine Data Leak

Moderna shares fell as much as 25% on Thursday after partial data on its closely watched melanoma vaccine leaked, setting off a steep selloff even as the full results later proved clinically meaningful and, by several analysts’ accounts, positive.

The personalized vaccine, known as intismeran autogene and developed with Merck, was tested alongside Merck’s immunotherapy Keytruda. Combined, the two cut the risk of recurrence or death in certain melanoma patients by 42% compared with Keytruda alone. The pairing also reduced the risk of the cancer spreading to distant parts of the body, or death, by 38%.

About 82% of patients who received the vaccine plus Keytruda were alive without their melanoma returning two years after treatment, versus 70% of those on Keytruda alone, the companies said. A separate analysis of the benefit after the six-month vaccine regimen showed a 58% reduction in risk of recurrence or death. The companies say it is still too early to know whether the treatment helps patients live longer overall.

The selloff, then, looks less like a verdict on the science and more like a reset of expectations. Moderna stock had climbed more than 530% year-to-date as of Thursday afternoon, leaving little room for anything short of a blowout. Merck, a far larger drugmaker, slipped about 1% on the day. Its shares are up nearly 41% this year.

Analysts leaned toward the data rather than the tape. BMO Capital Markets analyst Evan Seigerman called the reduction in recurrence or death clinically meaningful. In a research note, he wrote that the stock reaction “likely reflects inflated expectations into the full data release, rather than a true indictment on the efficacy of the combo therapy.” UBS analysts described it as “overall a strong data set” and said it adds confidence heading into upcoming studies in kidney and bladder cancers.

Dr. Hussein Tawbi, a melanoma expert and trial investigator at the University of Texas MD Anderson Cancer Center, called the results “a huge development for our patients.” He noted the added benefit comes with much milder toxicity, such as injection-site pain, than other cancer treatments.

Merck Research Laboratories President Dr. Dean Li said it can be harder to show additional benefit when a therapy is layered on top of something that already works well, like Keytruda. “We have no problems of showing additional benefit here,” he said ahead of the release. He also cautioned against getting ahead of the evidence. “Knocking one tree does not give you a cabin or a village,” Li said, acknowledging the companies still have to prove the approach works across tumor types. The pair are studying the vaccine in non-small cell lung cancer, bladder cancer and renal cell carcinoma.

The regulatory clock may be close. Moderna CEO Stéphane Bancel said the company is finishing a filing to seek full approval next year, calling it “a very, very happy moment for the field, for patients.” If approved, the shot would give Moderna a commercial product beyond its vaccines for Covid-19, the flu and respiratory syncytial virus.

The vaccine is built around each patient’s own tumor, targeting specific mutations to train the immune system, while Keytruda helps the body attack the cancer more effectively. That personalization carries a cost: the manufacturing process can take six weeks. Merck CEO Robert Davis told CNBC last week the company believes it can shorten that timeline, potentially getting the shot to more patients faster.

The detailed phase 3 results were scheduled for presentation at the European Society for Medical Oncology conference this weekend.