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Key Takeaways Merck's Q2 results on Aug. 4 will spotlight Keytruda, with consensus estimating sales at $8.06 billion.MRK expects continued demand across earlier-stage and metastatic cancers, plus higher Qlex contributions.MRK is expected to discuss long-term growth plans as Keytruda faces patent expiry and biosimilar competition. Merck’s (MRK - Free Report) blockbuster PD-1 inhibitor, Keytruda, approved for several types of cancer, is its key top-line driver, accounting for around 55% of the company’s pharmaceutical sales. Keytruda now holds more than 40 FDA-approved indications spanning 19 tumor types.

The drug has played an instrumental role in driving Merck’s steady revenue growth over the past few years. Keytruda is expected to remain Merck's primary growth driver in the second quarter of 2026. Investors will look out for Keytruda’s sales number when Merck announces second-quarter results on Aug. 4.

The Zacks Consensus Estimate for Keytruda’s sales is $8.06 billion. Keytruda is expected to continue delivering double-digit year-over-year growth in the second quarter. Its sales are likely to have been driven by strong demand across earlier-stage indications globally and continued strong momentum in metastatic indications. A favorable timing of wholesaler purchases benefited Keytruda’s sales in the first quarter, which is likely to be absent in the second.

Keytruda Qlex, the recently launched subcutaneous formulation of Keytruda, is also gradually contributing incremental sales. It added $128 million to Keytruda’s sales in the first quarter and the contribution is expected to be higher in the second.

Last quarter, Merck said that it was seeing an increase in usage of Keytruda in tumors that primarily affect women, including cervical, breast and endometrial cancers, as well as Keytruda in combination with Pfizer’s antibody drug conjugate, Padcev, in first-line, locally advanced or metastatic urothelial cancer. An update is expected on the upcoming conference call.

The company expects Keytruda’s growth to continue till it loses patent exclusivity in 2028. Keytruda’s core U.S. patent is expected to expire around 2028, with additional patents expiring slightly after that. Keytruda is expected to face significant biosimilar competition around 2028-2029. Once biosimilars enter, Keytruda’s sales are likely to decline sharply. Investors will also look for management commentary on long-term growth and Merck's strategy to offset Keytruda's LOE impact.

Key Competitors of Merck’s KeytrudaThe closest and most direct competitor to Keytruda is Bristol Myers’ (BMY - Free Report) Opdivo, another PD-1 inhibitor. Like Keytruda, Opdivo is approved across multiple tumor types, including non-small cell lung cancer (NSCLC), melanoma, renal cell carcinoma (RCC), head and neck cancer, bladder cancer and gastrointestinal cancers. Bristol Myers has strengthened Opdivo's competitive position through combination regimens such as Opdivo + Yervoy (ipilimumab) and newer fixed-dose combinations. Opdivo generated sales of $2.15 billion in the first quarter of 2026, down 5% year over year.

Another major competitor is AstraZeneca's (AZN - Free Report) PD-L1 inhibitor, Imfinzi, particularly in lung cancer. AstraZeneca’s Imfinzi generated sales of $1.69 billion in the first quarter of 2026, up 30% year over year.

Roche (RHHBY - Free Report) markets Tecentriq, another PD-L1 inhibitor competing with Keytruda in NSCLC, bladder cancer, liver cancer and certain breast cancers.

The longer-term competitive threat to Keytruda comes from dual PD-1/VEGF inhibitors that inhibit both the PD-1 pathway and the VEGF pathway at once. They are designed to overcome the limitations of single-target therapies like Keytruda. One of the most closely watched dual PD-1/VEGF inhibitor is Summit Therapeutics' ivonescimab, which it has licensed from Akeso.

MRK’s Price Performance, Valuation and EstimatesMerck’s stock has risen 21.7% so far this year compared with an increase of 10.5% for the industry.

Image Source: Zacks Investment Research

From a valuation standpoint, Merck is slightly expensive. Going by the price/earnings ratio, Merck’s shares currently trade at 19.04 forward earnings, higher than 18.49 for the industry as well as the stock’s five-year mean of 12.83.

Image Source: Zacks Investment Research

The Zacks Consensus Estimate for 2026 earnings has declined from $4.57 per share to $2.74 per share, while that for 2027 has declined from $9.81 per share to $9.72 per share over the past 30 days.

Image Source: Zacks Investment Research

Merck has a Zacks Rank #4 (Sell) at present.

You can see the complete list of today’s Zacks #1 Rank (Strong Buy) stocks here.

Phase 3 Trial Meets Primary Progression-Free Survival GoalThe trial met its primary endpoint of progression-free survival (PFS) for mismatch repair-deficient (dMMR) advanced or recurrent endometrial cancer patients who had not previously received systemic chemotherapy or who experienced recurrence more than six months after completing prior adjuvant therapy.

Keytruda is the first and only PD-1 inhibitor to show a statistically significant and clinically meaningful improvement in PFS as monotherapy compared to platinum doublet chemotherapy for these patients in a Phase 3 trial.

At a pre-specified interim analysis conducted by an independent Data Monitoring Committee, a trend toward improvement in overall survival (OS), the trial’s other primary endpoint, was observed for Keytruda.

However, these OS data were not mature at the time of this analysis.

Overall Survival Data Continue To MatureThe trial is ongoing, and OS for the full study population will be evaluated at a future analysis. The analysis also showed a clinically meaningful overall response rate (ORR), as well as complete response rate (CRR) and duration of response (DOR) for Keytruda.

The safety profile of Keytruda in this trial was consistent with that observed in previously reported studies; no new safety signals were identified.

In the U.S., Keytruda is the only anti-PD-1 therapy with three approved indications for patients with certain types of endometrial cancer.

Last week, the U.S. Food and Drug Administration (FDA) approved Merck’s Keytruda and Keytruda Qlex (pembrolizumab and berahyaluronidase alfa-pmph), each in combination with Padcev (enfortumab vedotin-ejfv), as neoadjuvant treatment. Then it continued after cystectomy as adjuvant treatment for muscle-invasive bladder cancer (MIBC).

These approvals represent the first and only PD-1 inhibitor plus antibody-drug conjugate regimens approved for adults with MIBC regardless of cisplatin eligibility.

MRK Price Action: Merck & Co shares were up 2.43% at $123.71 at the time of publication on Wednesday, according to Benzinga Pro data.

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Agreement will help state ADAP programs provide access to IDVYNSO™ (doravirine/islatravir) for eligible individuals

RAHWAY, N.J.--(BUSINESS WIRE)--Merck (NYSE: MRK), known as MSD outside of the United States and Canada, today announced an agreement with the ADAP Crisis Task Force (ACTF) to help state AIDS Drug Assistance Programs (ADAPs) provide access to the company’s new once-daily HIV treatment, IDVYNSO™ (doravirine/islatravir). In 2024, state ADAPs supported more than 250,000 people with HIV in the United States.

IDVYNSO was approved by the U.S. Food and Drug Administration (FDA) in April 2026 as a new, two-drug single-tablet regimen of 100 mg doravirine and 0.25 mg islatravir, for the treatment of HIV-1 infection in adults to replace the current antiretroviral regimen in those who are virologically suppressed (HIV-1 RNA less than 50 copies per mL) on a stable antiretroviral regimen with no history of virologic treatment failure and no known substitutions associated with resistance to doravirine.

“ADAP programs play a critical role in supporting access to treatment for people living with HIV who are uninsured or underserved,” said Tim Horn, Director, Medication Access, National Alliance of State and Territorial AIDS Directors (NASTAD). “We appreciate Merck’s continued engagement and its willingness to work collaboratively to help address the critical access challenges facing state ADAP programs.”

“Merck is pleased to have reached this agreement with the ADAP Crisis Task Force to expand access to IDVYNSO for eligible people with HIV,” said Conrod Kelly, U.S. HIV business unit head, Merck. “This agreement reflects our long-standing commitment to working with the ACTF, state ADAPs and the HIV community to strengthen access and help address persistent gaps in care.”

For individuals with questions about coverage and affordability, the Merck Access Program may be able to provide information about insurance benefits, estimated out-of-pocket costs and co-pay assistance options for eligible patients.

The Merck Access Program for IDVYNSO

Merck offers support to individuals who are prescribed IDVYNSO, including information about patient insurance coverage and out-of-pocket costs, co-pay assistance for eligible, commercially insured individuals, and how individuals may access IDVYNSO through The Merck Access Program. For additional information, healthcare providers and individuals can call 1-877-709-4455 or visit https://www.merckaccessprogram-idvynso.com/.

About IDVYNSO

IDVYNSO is a fixed-dose combination of two medicines, doravirine and islatravir. Doravirine is a non-nucleoside reverse transcriptase inhibitor (NNRTI) that inhibits HIV-1 replication by non-competitive inhibition of HIV-1 reverse transcriptase. Islatravir is a potent, next-generation nucleoside analog reverse transcriptase inhibitor (NRTI) that blocks HIV-1 replication by multiple mechanisms including:

inhibition of reverse transcriptase translocation, resulting in immediate chain termination, and induction of structural changes in the viral DNA (delayed chain termination). Selected Safety Information for IDVYNSO

Contraindications

IDVYNSO is contraindicated when co-administered with:

drugs that are strong cytochrome P450 (CYP)3A enzyme inducers as significant decreases in doravirine plasma concentrations may occur, which may decrease the effectiveness of IDVYNSO. lamivudine (3TC) or emtricitabine (FTC) as significant decreases in islatravir-triphosphate (ISL-TP) concentrations may occur, which may decrease the effectiveness of IDVYNSO. (See Drug Interactions) Warnings and Precautions

Severe skin reactions, including Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN), have been reported during postmarketing experience with doravirine-containing regimens. In addition, Drug Rash with Eosinophilia and Systemic Symptoms (DRESS syndrome) was reported with IDVYNSO in a clinical trial. Discontinue IDVYNSO, and other medications associated with these reactions, immediately if a painful rash with mucosal involvement, a progressive severe rash, or a rash with constitutional symptoms, eosinophilia, lymphadenopathy, or other organ involvement develops. Close clinical monitoring, and appropriate therapy should be initiated.

The concomitant use of IDVYNSO and certain other drugs may result in known or potentially significant drug interactions, some of which may lead to loss of therapeutic effect of IDVYNSO and possible development of resistance or possible clinically significant adverse reactions from greater exposures of a component of IDVYNSO.

Consider the potential for drug interactions prior to and during IDVYNSO therapy, review concomitant medications during IDVYNSO therapy, and monitor for adverse reactions. (See Drug Interactions)

Adverse Reactions

The most common adverse reactions (incidence ≥ 2%, all grades in any treatment group) reported in virologically suppressed participants in the IDVYNSO treatment groups in Trials 051 and 052, respectively, were: diarrhea (3% and 1%), dizziness (2% and 1%), fatigue (2% and 1%), abdominal distension (2% and 1%), headache (2% and 1%) and weight increased (2% and <1%).

A single case of severe immune thrombocytopenia (platelet count nadir of 2 x109/L) characterized by abrupt onset of subcutaneous hematoma, petechiae, and hematuria was reported in a participant 32 days after initiating IDVYNSO. The case resolved with discontinuation of IDVYNSO, in conjunction with treatments including corticosteroids and intravenous immunoglobulin (IVIG). Among all participants in Trials 052 and 051, there were no patterns of platelet decreases over time with IDVYNSO and no differences between treatment arms in mean change from baseline in platelet count.

Drug Interactions

IDVYNSO is a complete regimen; co-administration with other antiretroviral medications for treatment of HIV-1 infection is not recommended.

Co-administration of IDVYNSO with a CYP3A inducer decreases doravirine plasma concentrations, which may reduce the efficacy of IDVYNSO. If IDVYNSO is co-administered with rifabutin, one tablet of doravirine should be taken approximately 12 hours after the dose of IDVYNSO. Co-administration of IDVYNSO with other moderate CYP3A inducers is not recommended.

Co-administration of IDVYNSO and drugs that are inhibitors of CYP3A may result in increased plasma concentrations of doravirine.

Co-administration of IDVYNSO is not recommended with deoxycytidine kinase (dCK) substrates (e.g., nucleoside antimetabolites) as they may reduce the exposure of islatravir-triphosphate or with adenosine deaminase (ADA) inhibitors (e.g., pentostatin) as they may increase the exposure of islatravir. (see Contraindications)

Use in Specific Populations

There are insufficient human data on the use of IDVYNSO during pregnancy to inform a drug-associated risk of birth defects and miscarriage. Healthcare providers are encouraged to call the Antiretroviral Pregnancy Registry (APR) at 1-800-258-4263 to report pregnancy outcomes in individuals exposed to IDVYNSO.

It is unknown whether IDVYNSO or any of its components are present in human milk, affects human milk production, or has effects on the breastfed infant. Inform patients that the potential risks of breastfeeding include: (1) HIV-1 transmission (in infants without HIV-1), (2) developing viral resistance (in infants with HIV-1), and (3) serious adverse reactions in a breastfed infant similar to those seen in adults.

Clinical trials in virologically suppressed participants who received IDVYNSO included 81 (11%) participants aged 65 years and older, including 10 (1%) aged 75 years and older. Overall differences in response have not been identified between the elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out.

No dosage adjustment of IDVYNSO is required in patients with eGFR ≥30 mL/min/1.73 m2. IDVYNSO is not recommended in patients with eGFR <30 mL/min/1.73 m2 and has not been studied in participants undergoing dialysis.

No dosage adjustment of IDVYNSO is recommended in patients with mild or moderate hepatic impairment (Child- Pugh Class A or B). IDVYNSO has not been studied in patients with severe hepatic impairment (Child-Pugh Class C) and therefore is not recommended in these patients.

IDVYNSO does not have activity against hepatitis B virus (HBV). Patients with HBV coinfection who switch to IDVYNSO from an antiretroviral regimen with activity against HBV, and patients on IDVYNSO who are newly diagnosed with HBV coinfection, should be closely monitored and specific anti-HBV therapy should be considered, as clinically appropriate.

Merck’s Commitment to HIV

For 40 years, Merck has been committed to scientific research and discovery in HIV leading to scientific breakthroughs that have helped change HIV treatment. Our work has helped pioneer the development of new options across multiple drug classes to help those impacted by HIV. Today, we are developing a series of antiviral options designed to help people manage HIV and protect people from HIV. We are researching for real life and want to ensure people are not defined by HIV. Our work focuses on transformational innovations, collaborations with others in the global HIV community and access initiatives aimed at helping to end the HIV epidemic for everyone.

About Islatravir (MK-8591) and Merck’s HIV Research

Islatravir (MK-8591) is Merck’s potent, next-generation nucleoside analog reverse transcriptase inhibitor (NRTI) that blocks HIV-1 replication by multiple mechanisms including inhibition of reverse transcriptase translocation, resulting in immediate chain termination, and induction of structural changes in the viral DNA (delayed chain termination).

Islatravir is approved in combination with Merck’s NNRTI, doravirine, in the United States and Japan as IDVYNSO™, a once-daily, single-tablet regimen for the treatment of HIV-1 infection in adults to replace the current antiretroviral regimen in those who are virologically suppressed (HIV-1 RNA less than 50 copies per mL) on a stable antiretroviral regimen with no history of virologic treatment failure and no known substitutions associated with resistance to doravirine.

Islatravir is also under evaluation in multiple ongoing early and late-stage clinical trials in combination with other antiretrovirals for potential once-weekly treatments for HIV-1, in Merck's proprietary two-drug regimens.

Islatravir in combination with Gilead’s lenacapavir is in Phase 3 development as a novel oral once-weekly treatment for HIV-1 [ISLEND-1 (NCT06630286) and ISLEND-2 (NCT06630299)], and islatravir in combination with Merck’s investigational non-nucleoside reverse transcriptase inhibitor (NNRTI) ulonivirine (MK-8507) is in Phase 2b development (MK-8591B-060, NCT06891066 and MK-8591B-062, NCT07266831) as an oral once-weekly treatment.

MK-8527 is Merck’s investigational, novel, once-monthly, oral candidate for pre-exposure prophylaxis (PrEP) for HIV-1. In collaboration with the Gates Foundation, the Phase 3 EXPrESSIVE-10 trial (MK-8527-010, NCT07071623) trial is evaluating the safety and efficacy of MK-8527 as PrEP to reduce the risk of sexually acquired HIV-1 infection among women and adolescent girls in sub-Saharan Africa. The Phase 3 EXPrESSIVE-11 trial (MK-8527-011, NCT07044297) in 16 countries is evaluating the safety and efficacy of MK-8527 as PrEP to reduce the risk of sexually acquired HIV-1 infection among people likely to be exposed to HIV-1. Both trials are now enrolling.

For an overview of Merck’s HIV treatment and prevention clinical development program, please click here.

About Merck

At Merck, known as MSD outside of the United States and Canada, we are unified around our purpose: We use the power of leading-edge science to save and improve lives around the world. For more than 130 years, we have brought hope to humanity through the development of important medicines and vaccines. We aspire to be the premier research-intensive biopharmaceutical company in the world – and today, we are at the forefront of research to deliver innovative health solutions that advance the prevention and treatment of diseases in people and animals. We foster a diverse and inclusive global workforce and operate responsibly every day to enable a safe, sustainable and healthy future for all people and communities. For more information, visit www.merck.com and connect with us on X (formerly Twitter), Facebook, Instagram, YouTube and LinkedIn.

Forward-Looking Statement of Merck & Co., Inc., Rahway, N.J., USA

This news release of Merck & Co., Inc., Rahway, N.J., USA (the “company”) includes “forward-looking statements” within the meaning of the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995. These statements are based upon the current beliefs and expectations of the company’s management and are subject to significant risks and uncertainties. If underlying assumptions prove inaccurate or risks or uncertainties materialize, actual results may differ materially from those set forth in the forward-looking statements.

Risks and uncertainties include but are not limited to, general industry conditions and competition; general economic factors, including interest rate and currency exchange rate fluctuations; the impact of pharmaceutical industry regulation and health care legislation in the United States and internationally; global trends toward health care cost containment; technological advances, new products and patents attained by competitors; challenges inherent in new product development, including obtaining regulatory approval; the company’s ability to accurately predict future market conditions; manufacturing difficulties or delays; financial instability of international economies and sovereign risk; dependence on the effectiveness of the company’s patents and other protections for innovative products; and the exposure to litigation, including patent litigation, and/or regulatory actions.

The company undertakes no obligation to publicly update any forward-looking statement, whether as a result of new information, future events or otherwise. Additional factors that could cause results to differ materially from those described in the forward-looking statements can be found in the company’s Annual Report on Form 10-K for the year ended December 31, 2025 and the company’s other filings with the Securities and Exchange Commission (SEC) available at the SEC’s Internet site (www.sec.gov).

Please see Prescribing Information for IDVYNSO™ (doravirine and islatravir) at https://www.merck.com/product/usa/pi_circulars/i/idvynso/idvynso_pi.pdf and Patient Information for IDVYNSO at https://www.merck.com/product/usa/pi_circulars/i/idvynso/idvynso_ppi.pdf.

More News From Merck & Co., Inc.

RAHWAY, N.J.--(BUSINESS WIRE)--Merck (NYSE: MRK), known as MSD outside of the United States and Canada, today announced that the U.S. Food and Drug Administration (FDA) has approved an expanded indication for CAPVAXIVE® (Pneumococcal 21-valent Conjugate Vaccine) to include children and adolescents aged 2 through 17 years who have completed a primary pediatric pneumococcal vaccination series and have one or more chronic medical conditions that put them at an increased risk for pneumococcal disease. With this approval, CAPVAXIVE is the only PCV specifically indicated and studied in the U.S. for use in this patient population.

CAPVAXIVE is indicated for:

Active immunization for the prevention of invasive pneumococcal disease caused by Streptococcus pneumoniae serotypes 3, 6A, 7F, 8, 9N, 10A, 11A, 12F, 15A, 15B, 15C, 16F, 17F, 19A, 20A, 22F, 23A, 23B, 24F, 31, 33F and 35B in individuals 18 years of age and older and individuals 2 through 17 years of age who are at increased risk for pneumococcal disease; Active immunization for the prevention of pneumonia caused by S. pneumoniae serotypes 3, 6A, 7F, 8, 9N, 10A, 11A, 12F, 15A, 15C, 16F, 17F, 19A, 20A, 22F, 23A, 23B, 24F, 31, 33F and 35B in individuals 18 years of age and older. CAPVAXIVE should not be administered to individuals with a history of a severe allergic reaction (e.g., anaphylaxis) to any component of CAPVAXIVE or to diphtheria toxoid; see additional Select Safety Information below.

The indication for the prevention of pneumonia caused by S. pneumoniae serotypes 3, 6A, 7F, 8, 9N, 10A, 11A, 12F, 15A, 15C, 16F, 17F, 19A, 20A, 22F, 23A, 23B, 24F, 31, 33F, and 35B is approved under accelerated approval based on immune responses as measured by opsonophagocytic activity (OPA). Continued approval for this indication may be contingent upon verification and description of clinical benefit in a confirmatory trial.

“Children and adolescents with certain chronic conditions are at an increased risk for pneumococcal disease, including pneumonia, meningitis, and bloodstream infections,” said Dr. Rotem Lapidot, Chief of Pediatric Infectious Diseases at Rambam Health Care Campus, investigator, STRIDE-13 trial. “This approval recognizes the potential of CAPVAXIVE to deliver additional protection by including serotypes not contained in approved primary pediatric PCV series, and represents a new approach to helping protect children and adolescents at increased risk for pneumococcal disease.”

The approval is based on data from the Phase 3 STRIDE-13 trial, which evaluated CAPVAXIVE compared to PPSV23 (pneumococcal 23-valent polysaccharide vaccine) in children and adolescents aged 2 through 17 years who completed a primary pediatric pneumococcal vaccination series and have one or more chronic medical conditions that put them at an increased risk of pneumococcal disease. See “STRIDE-13 Clinical Data Supporting Approval” below for additional details.

“While CAPVAXIVE was specifically designed for adults, it may also offer additional disease protection for this specific population of children and adolescents, when given after the primary pediatric pneumococcal vaccination series,” said Dr. Paula Annunziato, senior vice president, infectious diseases and vaccines, global clinical development, Merck Research Laboratories. “The approval of CAPVAXIVE for children and adolescents at increased risk for pneumococcal disease demonstrates our commitment to addressing this disease in people of all ages, not only addressing an unmet need, but also reinforcing Merck’s longstanding commitment to public health and infectious diseases.”

The expanded indication for CAPVAXIVE complements existing primary pediatric pneumococcal vaccination series for children and adolescents at increased risk for pneumococcal disease. According to a 2025 study of 2015-2019 CDC ABC surveillance data, including three groups, one of which consisted of children <18 years old (age range 31 to 109 months; n=219) with at least one risk condition for invasive pneumococcal disease (IPD) such as chronic heart disease, chronic lung disease, diabetes, and chronic kidney disease, CAPVAXIVE covers the serotypes responsible for ~79% of IPD cases. In this risk group, the 11 unique serotypes covered by CAPVAXIVE account for ~40% of IPD cases. These values are based on CDC epidemiologic data and do not reflect the efficacy of CAPVAXIVE. There are currently no studies evaluating the efficacy of CAPVAXIVE.

About CAPVAXIVE

CAPVAXIVE is Merck’s 21-valent pneumococcal conjugate vaccine indicated for active immunization for the prevention of invasive disease and pneumonia in adults 18 years of age and older and for the prevention of invasive disease in children and adolescents aged 2 through 17 years who have one or more chronic medical conditions that put them at an increased risk of pneumococcal disease. CAPVAXIVE was specifically designed to help address the Streptococcus pneumoniae serotypes predominantly responsible for IPD in adults, including eight unique serotypes, 15A, 15C, 16F, 23A, 23B, 24F, 31 and 35B compared to other approved pneumococcal vaccines. CAPVAXIVE is administered as a single dose.

CAPVAXIVE helps provide coverage against the serotypes responsible for approximately 82% of IPD cases in adults 50 years of age and older, compared to ~54% by PCV20, based on national-level CDC data from 2019-2023. These values are based on CDC epidemiologic data and do not reflect the efficacy of the respective vaccines. There are currently no studies comparing the efficacy of CAPVAXIVE and PCV20.

With this approval, CAPVAXIVE is also indicated for the prevention of invasive disease in children and adolescents aged 2 through 17 years who have one or more chronic medical conditions that put them at an increased risk for pneumococcal disease.

Select Safety Information for CAPVAXIVE in Children and Adolescents at Increased Risk for Pneumococcal Disease in the U.S.

Do not administer CAPVAXIVE to individuals with a history of a severe allergic reaction (e.g., anaphylaxis) to any component of CAPVAXIVE or to diphtheria toxoid.

Syncope may occur with administration of injectable vaccines.

Individuals with altered immunocompetence, including those receiving immunosuppressive therapy, may have a reduced immune response to CAPVAXIVE.

The most commonly reported (>10%) solicited adverse reactions in individuals 18 through 49 years of age who received CAPVAXIVE were: injection-site pain (73.1%), fatigue (36.0%), headache (27.5%), myalgia (16.4%), injection-site erythema (13.8%), and injection-site swelling (13.3%).

The most commonly reported (>10%) solicited adverse reactions in individuals 50 years of age and older who received CAPVAXIVE were: injection-site pain (41.2%), fatigue (19.7%), and headache (11.0%).

The most commonly reported (>10%) solicited adverse reactions in individuals 2 through 17 years of age who are at increased risk for pneumococcal disease were: injection-site pain (67.7%), injection-site erythema (24.3%), fatigue (20.1%), injection-site swelling (18.8%), headache (17.1%), malaise (13.3%), and irritability (11.6%).

Vaccination with CAPVAXIVE may not protect all vaccine recipients.

STRIDE-13 Clinical Data Supporting Approval

STRIDE-13 (NCT06177912) is a randomized, double-blind, active comparator-controlled Phase 3 study that evaluated individuals 2 through 17 years of age with one or more prespecified medical conditions (diabetes mellitus, chronic heart disease, chronic kidney disease, chronic liver disease, chronic lung disease) known to increase the risk of pneumococcal disease and who have previously completed a primary pneumococcal vaccination regimen at least 8 weeks prior to enrollment (n=874). Participants were randomized 3:2 to receive a single dose of CAPVAXIVE (n=527) or PPSV23 (n=347). Results from the study include:

CAPVAXIVE was noninferior to PPSV23 for the 12 shared serotypes and induced statistically significantly greater OPA GMTs compared to PPSV23 for the 9 serotypes unique to CAPVAXIVE; CAPVAXIVE also elicited immune responses to serotype 15B (cross-reactive to serotype 15C). In a post hoc analysis utilizing the same prespecified noninferiority criterion that was used for the shared serotypes, CAPVAXIVE was noninferior to PPSV23 for serotype 15B; The safety profile of CAPVAXIVE was generally comparable to PPSV23. Solicited adverse reactions following administration of CAPVAXIVE lasted a median of 2 days with most reactions lasting ≤3 days; The proportion of individuals reporting 1 or more serious adverse events (SAE) within 6 months postvaccination was 5.5% (n=29) in individuals vaccinated with CAPVAXIVE and 7.2% (n=25) in individuals vaccinated with PPSV23. There were no notable patterns or imbalances between vaccine groups for SAEs. One individual (0.2%) who received CAPVAXIVE had an SAE considered related to vaccination. This SAE was syncope (Grade 2, required hospitalization) and occurred approximately 3 minutes postvaccination. About Pneumococcal Disease

Pneumococcal disease is an infection caused by bacteria called Streptococcus pneumoniae. There are about 100 different types (referred to as serotypes) of pneumococcal bacteria, which can affect adults differently than children. Pneumococcal disease can be invasive or non-invasive. Non-invasive pneumococcal illnesses include pneumonia (when pneumococcal disease is confined to the lungs), whereas invasive pneumococcal illnesses include pneumococcal bacteremia (infection in the bloodstream), bacteremic pneumococcal pneumonia (pneumonia with bacteremia) and pneumococcal meningitis (infection of the coverings of the brain and spinal cord).

About Merck

At Merck, known as MSD outside of the United States and Canada, we are unified around our purpose: We use the power of leading-edge science to save and improve lives around the world. For more than 130 years, we have brought hope to humanity through the development of important medicines and vaccines. We aspire to be the premier research-intensive biopharmaceutical company in the world – and today, we are at the forefront of research to deliver innovative health solutions that advance the prevention and treatment of diseases in people and animals. We foster a diverse and inclusive global workforce and operate responsibly every day to enable a safe, sustainable and healthy future for all people and communities. For more information, visit www.merck.com and connect with us on X (formerly Twitter), Facebook, Instagram, YouTube and LinkedIn.

Forward-Looking Statement of Merck & Co., Inc., Rahway, N.J., USA

This news release of Merck & Co., Inc., Rahway, N.J., USA (the “company”) includes “forward-looking statements” within the meaning of the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995. These statements are based upon the current beliefs and expectations of the company’s management and are subject to significant risks and uncertainties. There can be no guarantees with respect to pipeline candidates that the candidates will receive the necessary regulatory approvals or that they will prove to be commercially successful. If underlying assumptions prove inaccurate or risks or uncertainties materialize, actual results may differ materially from those set forth in the forward-looking statements.

Risks and uncertainties include but are not limited to, general industry conditions and competition; general economic factors, including interest rate and currency exchange rate fluctuations; the impact of pharmaceutical industry regulation and health care legislation in the United States and internationally; global trends toward health care cost containment; technological advances, new products and patents attained by competitors; challenges inherent in new product development, including obtaining regulatory approval; the company’s ability to accurately predict future market conditions; manufacturing difficulties or delays; financial instability of international economies and sovereign risk; dependence on the effectiveness of the company’s patents and other protections for innovative products; and the exposure to litigation, including patent litigation, and/or regulatory actions.

The company undertakes no obligation to publicly update any forward-looking statement, whether as a result of new information, future events or otherwise. Additional factors that could cause results to differ materially from those described in the forward-looking statements can be found in the company’s Annual Report on Form 10-K for the year ended December 31, 2025 and the company’s other filings with the Securities and Exchange Commission (SEC) available at the SEC’s Internet site (www.sec.gov).

Please see the Prescribing Information for CAPVAXIVE (Pneumococcal 21-valent Conjugate Vaccine) at https://www.merck.com/product/usa/pi_circulars/c/capvaxive/capvaxive_pi.pdf and the Patient Information/Medication Guide for CAPVAXIVE at https://www.merck.com/product/usa/pi_circulars/c/capvaxive/capvaxive_ppi.pdf .

More News From Merck & Co., Inc.