Key Highlights

● Merck closed at $147.24 on October 22, among the Dow's decliners.

● The Phase 3 trial tested the vaccine alongside Merck's Keytruda in over 1,100 patients.

● The hazard ratio for recurrence or death was 0.58.

● Full data will be presented Saturday at the ESMO cancer conference.

Merck (NYSE:MRK) fell on Thursday, October 22, 2026, closing at $147.24 and finishing among the decliners on the Dow Jones Industrial Average, even as the broader health care sector climbed to a record.

The drugmaker's dip was tied to its partnership with Moderna (NASDAQ:MRNA) on an experimental cancer vaccine. Late-stage data from the program appeared before its scheduled presentation, and investors treated the results as a sell-the-news event.

What the data showed

The Phase 3 INTerpath-001 trial tested intismeran, Moderna's individualized mRNA cancer vaccine, in combination with Merck's blockbuster immunotherapy Keytruda in more than 1,100 patients with high-risk melanoma.

According to the reported results, the combination reduced the risk of recurrence or death, with a hazard ratio of 0.58. It also lowered the risk of distant metastasis or death. However, the reduction in recurrence risk was smaller than the one seen in the earlier Phase 2b study, based on the reported figures.

The full data is due Saturday at the ESMO cancer conference in Madrid.

Analysts: good data, tough reaction

Analysts generally described the results positively, while noting the stock reaction. A UBS analyst called it "solid data" and a "sell the news" event. A William Blair analyst similarly described the data as great but said the market treated it as a sell-the-news moment. TD Cowen called the results compelling.

For Moderna, the reaction was severe. Its shares closed at $202.63 and were one of the weakest performers in the S&P 500. Intraday, the decline was deep enough that it would have been the stock's steepest one-day drop on record. About $24 billion in market value was erased. The drop came after a huge run for Moderna's shares this year.

Merck's decline was far more modest. The vaccine is one of many programs at the company, and Keytruda remains its core franchise.

Health care still hit a record

Merck's dip stood out because the rest of health care rallied. The S&P 500 health care sector hit a record despite Moderna's slide, with Johnson & Johnson (NYSE:JNJ) and Amgen (NASDAQ:AMGN) among the gainers on the Dow.

The sector benefited from a rotation out of technology. Artificial-intelligence and chip stocks sold off after Meta Platforms (NASDAQ:META) laid out heavy spending plans and Lam Research (NASDAQ:LRCX) flagged supply constraints. The Nasdaq Composite fell 694.00 points, and the S&P 500 lost 93.74 points to 7,663.43, its worst day since July.

The Dow Jones Industrial Average finished up 11.89 points at 52,867.98, essentially flat and at a one-month high, according to market data, as Procter & Gamble (NYSE:PG), Home Depot (NYSE:HD) and Johnson & Johnson rallied.

About two of every three S&P 500 stocks rose, according to market reports, and Treasury yields fell sharply, with the 10-year yield closing back below a closely watched threshold for the first time since September 22.

Merck Awaits the Full INTerpath-001 Presentation

The full INTerpath-001 presentation at ESMO on Saturday is the next big event for Merck and Moderna. Investors will look for details on safety, the durability of the benefit and how the results compare across patient groups. Any regulatory timeline for the combination would also be closely watched. More broadly, the Federal Reserve's decision on October 28 and next week's big tech earnings will shape whether money keeps rotating into health care.