Merck Announces Topline Results from Phase 2b/3 Trial of Clesrovimab (MK-1654), an Investigational Respiratory Syncytial Virus Preventative Monoclonal Antibody for Infants

Clesrovimab met all primary safety and efficacy endpoints

Merck (NYSE: MRK), known as MSD outside of the United States and Canada, today announced positive topline results from its Phase 2b/3 clinical trial (MK-1654-004) evaluating clesrovimab (MK-1654), the company’s investigational prophylactic monoclonal antibody designed to protect infants from respiratory syncytial virus (RSV) disease. In the trial, clesrovimab met its primary safety and efficacy endpoints, including reducing medically attended lower respiratory infections (MALRI) caused by RSV through Day 150. Detailed findings of the study will be presented at an upcoming scientific congress and Merck plans to file these data with global regulatory authorities.

“RSV is highly contagious and can cause inflammation in the airways of infants leading to difficulty breathing. As a widespread illness globally, RSV is the leading cause of hospitalization for healthy infants,” said Dr. Paula Annunziato, senior vice president, infectious diseases and vaccines, Global Clinical Development, Merck Research Laboratories. “We are encouraged by these findings and look forward to working with regulators to provide a new option to help address the impact of RSV on infants and their families."

About MK-1654-004

MK-1654-004 (NCT04767373) is a Phase 2b/3 double-blind, randomized, placebo-controlled study to evaluate the safety and efficacy of clesrovimab in healthy preterm and full-term infants. Participants were randomized to receive either a single dose of clesrovimab or placebo. The primary endpoints include the incidence of participants with RSV-associated medically attended lower respiratory infection (MALRI) from Day 1 (post dose) to Day 150 as compared to placebo and safety. Safety measures assessed included the percentage of participants with any injection-related adverse events (AEs), AEs of special interest (AESIs) solicited systemic AEs, or serious adverse events (SAEs).

About Clesrovimab (MK-1654)

Clesrovimab (MK-1654) is an investigational extended half-life monoclonal antibody (mAb) developed as a passive immunization for the prevention of RSV-associated medically attended lower respiratory infection (MALRI). Clesrovimab is being studied in infants (pre-term and full-term) to provide rapid, durable protection through their first RSV season with a single, fixed-dose administration.

About RSV

Respiratory syncytial virus (RSV) is a contagious virus that causes widespread seasonal infection with a worldwide burden in infants and older adults. There is high unmet need for preventative options in both healthy and high-risk infants. Globally, it is the leading cause of hospitalization for healthy infants under a year old. RSV can lead to serious respiratory conditions like bronchiolitis and pneumonia, causing an estimated 101,000 deaths a year worldwide in children under five.

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, 2023 and the company’s other filings with the Securities and Exchange Commission (SEC) available at the SEC’s Internet site (www.sec.gov).

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