New York, Jan 7, 2026, 18:52 EST — After-hours
- Merck shares eased in extended trading after U.S. health officials shifted HPV vaccine guidance to a single dose
- Analysts flagged a potential hit to Gardasil volumes and 2026 revenue expectations
- Merck also closed its Cidara acquisition and set a Feb. 3 date for quarterly results
Merck & Co (MRK.N) shares edged down in after-hours trading on Wednesday after U.S. health officials updated the childhood immunization schedule and moved to a single dose for the human papillomavirus (HPV) vaccine, a change that could pressure demand for Merck’s Gardasil shot. The stock was down about 0.2% at $108.60, after trading between $107.99 and $111.42 in the regular session. HHS.gov
The CDC move lands at an awkward moment for Merck, which relies on Gardasil as its biggest vaccine franchise and a key growth lever alongside cancer drug Keytruda. Jefferies analyst Akash Tewari estimated the schedule change could trim Gardasil sales by $315 million to $630 million in 2026, with a FactSet consensus previously putting Gardasil revenue around $5.2 billion, MarketWatch reported; Gardasil sales fell 25% to $1.7 billion in the third quarter, pressured by China demand and competition. MarketWatch
The CDC said it will keep the schedule in three buckets — vaccines for all children, for certain high-risk groups, and for “shared clinical decision-making” — and said insurers must still cover the listed shots without cost-sharing. Acting CDC Director Jim O’Neill said the agency accepted recommendations for a “more focused schedule,” while ABC News reported that “shared clinical decision-making” means parents and clinicians talk through whether a vaccine makes sense, as some shots including influenza, rotavirus and COVID-19 were stripped of universal recommendations. CDC+1
Merck, separately, said it completed its cash tender offer for Cidara Therapeutics at $221.50 a share and expects the deal to lift 2026 research and development expense by about $9.0 billion, or roughly $3.65 per share, in both GAAP results (standard accounting) and the adjusted figures it also reports. Chief executive Robert Davis said the acquisition “strengthens and complements our expanding respiratory portfolio” and pointed to CD388, a “potentially first-in-class, long-acting antiviral” for influenza prevention; Merck announced the nearly $9.2 billion deal in November as it looked to diversify ahead of Keytruda patent losses later this decade. Merck.com
On the pipeline, Merck said it initiated a Phase 3 trial of calderasib (MK-1084), an oral KRAS G12C inhibitor, in combination with KEYTRUDA QLEX — a subcutaneous, under-the-skin form of Keytruda — for certain patients with advanced non-small cell lung cancer. Merck’s Gregory Lubiniecki said the study will test a chemo-free combination that “may help improve outcomes”; the main endpoint is progression-free survival, a measure of how long patients live without their cancer worsening. Merck.com
Merck will report fourth-quarter and full-year 2025 results on Feb. 3 and hold a conference call at 9 a.m. ET. Investors will be listening for how Merck frames U.S. vaccine demand after the CDC shift and how it threads the Cidara accounting charge into its 2026 outlook. Merck.com
But the new vaccine schedule could prove messy in practice. Public health experts criticized the overhaul, and some doctors said they plan to keep following American Academy of Pediatrics guidance — which could soften the near-term hit to volumes, or just leave families confused and decisions delayed. CIDRAP
Merck’s next hard catalyst is Feb. 3, when it reports results and updates guidance as investors gauge whether vaccine policy, pricing and portfolio moves are starting to collide in the numbers.
