Moderna falls up to 25% as elevated expectations overshadow positive cancer vaccine data

Moderna (MRNA) shares declined by as much as 25% on Thursday, even though the cancer vaccine data was positive. In certain patients, the injection reduced the risk of melanoma returning or death by 42%.

Parts of the data were leaked prior to the full announcement. Despite the decline, the stock remains up over 530% year-to-date for 2026 as of Thursday afternoon, according to CNBC.

How high were the expectations set for the cancer vaccine?

Merck, a considerably larger pharmaceutical company, dropped roughly 1% and has gained about 41% this year. In comparison, Moderna's 2026 stock surge exceeds 530%.

BMO Capital Markets analyst Evan Seigerman stated that the sell-off probably mirrors inflated expectations prior to the announcement. He did not interpret it as a judgment on the combination's efficacy.

Meanwhile, analysts at UBS described the outcomes as robust, adding that expectations could account for the market's response.

Intismeran autogene is a customized vaccine targeting mutations in a patient's tumor. It is used in combination with Keytruda, Merck's immunotherapy drug.

Roughly 82% of patients receiving the combination were alive with no recurrence at the two-year mark, compared to 70% who had Keytruda only. The combination also lowered the risk of metastasis or death by 38%.

Can a single melanoma success justify the broader stock surge?

However, the study looked at only one cancer type. Dean Li, president of Merck Research Laboratories, acknowledged that additional work is necessary to demonstrate the vaccine's effectiveness across different cancers.

The firms are testing the vaccine in other cancer types, such as lung, bladder, and kidney cancers.

Positive results could provide Moderna with a commercially viable product beyond its current lineup of Covid-19, flu, and RSV vaccines.

Manufacturing poses a hurdle, as each customized dose can require six weeks to prepare.

Personalized vaccines also rely on tumor sequencing.

Nevertheless, Merck CEO Robert Davis told CNBC that the company thinks it can reduce the production time, enabling faster access for patients.

Currently, the companies state that it is premature to evaluate overall survival. Complete phase 3 data is scheduled to be presented at the ESMO conference this weekend.

The industry's upcoming test is whether personalized medicine can be manufactured quickly enough to satisfy investor expectations.