Merck Reports Positive Phase 3 Trial Results for ENFLONSIA in RSV Prevention
Written by Emily J. Thompson, Senior Investment Analyst
Updated: 1 hour ago
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Should l Buy MRK?
Source: Businesswire
- Positive Trial Results: Merck presented findings from the Phase 3 SMART trial of ENFLONSIA (clesrovimab) at the RSVVW’26 conference in Rome, indicating consistent safety and efficacy in high-risk children, supporting global regulatory submissions.
- Safety Consistency: In the second RSV season, adverse reactions such as injection site erythema and fever were comparable to the first season, confirming the drug's safety profile in vulnerable populations and suggesting potential for additional protection.
- Efficacy Support: Results from the SMART trial demonstrated that a single dose of ENFLONSIA provides up to five months of protection in high-risk children, with a 3.0% RSV-related hospitalization rate in the second season, highlighting its preventive potential against severe RSV disease.
- Global Regulatory Submission: Merck plans to share the second season results with the FDA and global regulatory authorities to seek an expanded indication for ENFLONSIA in high-risk children, further solidifying its critical role in RSV prevention.
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Analyst Views on MRK
Wall Street analysts forecast MRK stock price to fall
16 Analyst Rating
11 Buy
5 Hold
0 Sell
Moderate Buy
Current: 121.570
Low
95.00
Averages
119.53
High
139.00
Current: 121.570
Low
95.00
Averages
119.53
High
139.00
About MRK
Merck & Co., Inc. is a global health care company that delivers health solutions through its prescription medicines, including biologic therapies, vaccines and animal health products. Its Pharmaceutical segment includes human health pharmaceutical and vaccine products. The Company sells its human health pharmaceutical products primarily to drug wholesalers and retailers, hospitals, government agencies and managed health care providers. It sells these human health vaccines primarily to physicians, wholesalers, distributors and government entities. Its Animal Health segment discovers, develops, manufactures and markets a range of veterinary pharmaceutical and vaccine products, as well as health management solutions and services, for the prevention, treatment and control of disease in all livestock and companion animal species. Its products include KEYTRUDA (pembrolizumab) injection, for intravenous use; WELIREG (belzutifan) tablets, for oral use; Ohtuvayre (ensifentrine) and others.
About the author

Emily J. Thompson
Emily J. Thompson, a Chartered Financial Analyst (CFA) with 12 years in investment research, graduated with honors from the Wharton School. Specializing in industrial and technology stocks, she provides in-depth analysis for Intellectia’s earnings and market brief reports.
- Positive Trial Results: Merck's Phase 3 SMART trial for ENFLONSIA (clesrovimab) in high-risk infants and children reported positive outcomes, indicating consistent safety during the second RSV season compared to the first, suggesting potential efficacy in this demographic.
- Safety Consistency: The safety profile observed in children under 2 years receiving ENFLONSIA aligns with that seen in the MK-1654-007 trial, reinforcing confidence in the drug's application for high-risk pediatric patients.
- Similar Antibody Concentrations: The monoclonal antibody serum concentrations in high-risk children under 2 years were comparable to those in healthy infants from the pivotal Phase 2b/3 CLEVER trial, indicating ENFLONSIA's potential effectiveness in this vulnerable population.
- Efficacy Extrapolation Support: Results from the SMART study support the extrapolation of ENFLONSIA's efficacy to children under 2 years at increased risk for severe RSV disease, enhancing Merck's competitive position in the RSV treatment market and laying a foundation for future clinical applications.
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- Positive Trial Results: Merck presented findings from the Phase 3 SMART trial of ENFLONSIA (clesrovimab) at the RSVVW’26 conference in Rome, indicating consistent safety and efficacy in high-risk children, supporting global regulatory submissions.
- Safety Consistency: In the second RSV season, adverse reactions such as injection site erythema and fever were comparable to the first season, confirming the drug's safety profile in vulnerable populations and suggesting potential for additional protection.
- Efficacy Support: Results from the SMART trial demonstrated that a single dose of ENFLONSIA provides up to five months of protection in high-risk children, with a 3.0% RSV-related hospitalization rate in the second season, highlighting its preventive potential against severe RSV disease.
- Global Regulatory Submission: Merck plans to share the second season results with the FDA and global regulatory authorities to seek an expanded indication for ENFLONSIA in high-risk children, further solidifying its critical role in RSV prevention.
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- Clinical Trial Results: At the 9th RSVVW Conference, Merck announced positive findings for ENFLONSIA (clesrovimab) during the second RSV season, demonstrating consistent safety and efficacy in high-risk infants, supporting global regulatory submissions.
- Safety Analysis: In the second RSV season, adverse reactions such as injection site erythema and fever were low among children receiving ENFLONSIA, indicating good safety in vulnerable populations and potential for additional protection.
- Serum Concentration Comparison: The serum concentrations of ENFLONSIA in high-risk children were similar to those in healthy infants from the pivotal CLEVER trial, further validating its potential in preventing severe RSV disease and supporting future treatment options.
- Market Outlook: Merck aims to expand ENFLONSIA's availability to all eligible high-risk children globally, with FDA approval anticipated in 2025, marking a significant advancement in RSV prevention efforts.
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- Breakthrough Therapy Designation: The FDA has granted Breakthrough Therapy Designation for Rybrevant (amivantamab and hyaluronidase-lpuj) as a monotherapy for adults with advanced head and neck squamous cell carcinoma, applicable to patients with recurrent or metastatic disease after progression on platinum-based chemotherapy and a PD-1 or PD-L1 inhibitor, indicating strong recognition and market potential for the new therapy.
- Contract Extension: The collaboration agreement signed by Johnson & Johnson in January 2025 has been extended to mid-2026 under the same economic terms, including a fixed monthly management fee, driven by strong engagement and satisfaction metrics, reflecting ongoing confidence in the program's performance.
- Market Model Development: Trellus Health CEO Marla Dubinsky stated that the company is establishing a scalable go-to-market model for pharmaceuticals, focusing on disciplined execution, recurring revenue growth, and expansion in immunology and inflammation, showcasing a positive outlook for future developments.
- Financial Outlook: Trellus Health expects fiscal 2025 revenue to be approximately $545,000 and has reduced its monthly cash burn to around $400,000, demonstrating improved financial management and confidence in future growth prospects.
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- Strategic Collaboration: Merck has signed a research and development agreement with Mayo Clinic to leverage artificial intelligence and multimodal clinical data to accelerate drug discovery and development, marking Mayo Clinic's first strategic collaboration of this scale with a global biopharmaceutical company.
- Data Integration Advantage: By integrating Mayo Clinic's clinical and genomic datasets, Merck aims to enhance disease understanding and target identification using AI technologies, thereby improving the success rate of early development decisions and driving more effective personalized treatment options.
- Focus on High-Need Areas: The collaboration will initially target high-need therapeutic areas across three specialties, utilizing advanced analytics and multimodal approaches to advance the development of more effective therapies, reflecting a shared focus on applying cutting-edge technologies.
- Potential for Innovative Breakthroughs: Merck's CEO Robert M. Davis stated that by collaborating with Mayo Clinic, both parties will combine high-quality clinical data and AI insights to enhance the probability of success in drug development, ultimately accelerating the delivery of innovative therapies to patients.
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Health Canada Approval: Health Canada has approved Keytruda (pembrolizumab) as a subcutaneous formulation for multiple cancer indications.
Treatment Options: This approval expands treatment options for patients with various types of cancer, enhancing accessibility and convenience in administration.
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