Moderna's stock price fell by 25% on Thursday, following the leakage of some data regarding a cancer vaccine that it was developing in collaboration with Merck, which had attracted significant attention.

Nevertheless, the complete data released later on Thursday appears to be meaningful for patients and is more positive than Wall Street's expectations. This personalized vaccine, named intismeran autogene, when used in combination with Merck's immunotherapy Keytruda, reduced the risk of recurrence or death by 42% in some melanoma patients compared to using Keytruda alone.

Data shows that when this vaccine is used in conjunction with Keytruda, it also reduces the risk of cancer spreading to distant parts of the body or death by 38% compared to using this immunotherapy alone.

The company stated that among patients who received the personalized cancer vaccine plus Keytruda treatment, approximately 82% were still alive after two years with no recurrence of melanoma; whereas for patients who only received Keytruda, this proportion was 70%.

The results of these detailed phase 3 trials were originally scheduled to be announced at the European Society for Medical Oncology conference this weekend.

Several analysts admitted that investors' expectations had been raised before the release of the results, but they stated that the data overall was positive.

"We believe that the relative decrease in relapse/death rates is clinically significant," said analyst BMO Capital Markets Evan Seigerman in a research report on Thursday. "This response is likely to reflect overly high expectations before the release of the complete data, rather than truly negating the efficacy of this combination therapy."

Investors believe that this targeted vaccine could become a breakthrough therapy and may also be used for other types of cancer in the future. It could also bring a key new commercial product to the product pipeline of Moderna, which already has COVID-19 vaccines, influenza vaccines, and respiratory syncytial virus vaccines in its portfolio.

UBS Analysts stated in a research report on Thursday that this is "overall a set of strong data," which has given the market more confidence in subsequent studies of the vaccine for kidney cancer and bladder cancer. They added that the stock price reaction may be more due to overly high expectations rather than the data being disappointing.

High market expectations for this product have driven the Moderna stock price to rise significantly this year. As of Thursday afternoon, the stock's cumulative increase for the year has exceeded 530%.

Merck's stock price fell by about 1% on Thursday. The stock price of this larger pharmaceutical company has risen by nearly 41% so far this year.

Since this is a personalized vaccine, the complex production process may take up to six weeks. However, Merck's CEO Robert Davis stated last week to CNBC that the company believes it will be possible to shorten this time in the future, which could potentially allow more patients to receive the vaccine more quickly.