"RSV prevention option for infants has been added"

'Enflonsia' approved in South Korea… the preventive effect is maintained with a single injetion

A treatment has been added after ''Beyfortus'…hospitalization burden is expected to be alleviated

A new treatment option has entered South Korea's infant respiratory syncytial virus (RSV) prophylaxis market.

Following domestic regulatory authorization of MSD Korea's long-acting antibody injection 'Enflonsia (clesrovimab)', competition in the infant RSV market is set to intensify alongside Sanofi and AstraZeneca's 'Beyfortus (nirsevimab)'.

On the 29th, MSD Korea hosted a press conference at The Plaza Hotel in Jung-gu, Seoul, to celebrate the domestic approval of Enflonsia.

Professor Ki Wook Yoon of the Department of Pediatrics at Seoul National University College of Medicine

Enflonsia was approved in South Korea on the 1st of last month as a long-acting preventive monoclonal antibody indicated for the prevention of RSV-induced lower respiratory tract disease (LRTD) in newborns and infants.  

The antibody is distinguished by its fixed-dose administration design, which requires no weight-based dosage adjustments. Providing sustained protective efficacy for 5 to 6 months post-injection, a single dose delivers comprehensive coverage throughout an entire RSV epidemic season.

In South Korea, RSV typically peaks between October and March. Enflonsia can be administered immediately at birth for newborns during the active season, or as a single dose before the start of the first RSV season for infants born during off-season months.  

RSV infections initially present with mild, cold-like symptoms. The infections frequently progress to severe lower respiratory tract complications, such as acute bronchiolitis and pneumonia, in infants under one year of age, often requiring emergency intervention and inpatient hospitalization.

Professor Ki Wook Yoon of the Department of Pediatrics at Seoul National University College of Medicine (Public Relations Director of the Korean Society of Pediatric Infectious Diseases) stated, "Young infants are exceptionally vulnerable to severe RSV disease due to their immature immune systems and narrow airway anatomy," and added, "When infection progresses to severe lower respiratory disease requiring medical management, the clinical burden centers heavily on acute hospitalizations."

Professor Yoon added, "Infant RSV prophylaxis strategies must expand beyond simply blocking initial transmission to substantially mitigating the burdens experienced by pediatric patients and their families, including acute hospital admissions and severe lower respiratory tract illness."

According to a nationwide Korean study (2007–2019) published last year, which analyzed National Health Insurance (NHI) claims data, 44.7% of pediatric RSV cases in South Korea under age 5 required hospitalization.

Infants aged 6 to 11 months were the most heavily impacted cohort, accounting for 48.2% of total RSV hospitalizations and 57.3% of intensive care unit (ICU) admissions among children under 5. Infants under 6 months of age demonstrated the longest average hospital stay at approximately 8.35 days.

In the Phase 2b/3 CLEVER clinical trial, a single dose of Enflonsia reduced the incidence of RSV-associated medically attended lower respiratory tract infections by 60.5%. It decreased the risk of RSV-associated hospitalizations by 84.3%.

Furthermore, in the Phase 3 SMART trial evaluating high-risk infants and young children, Enflonsia demonstrated a safety profile comparable to the existing standard-of-care RSV antibody, 'Synagis (palivizumab)', confirming consistent preventive efficacy.

Professor Yoon noted, "Because the burden of RSV hospitalizations and severe lower respiratory tract disease concentrates heavily during an infant's first year of life, evaluation of preventive interventions must consider how effectively they reduce medically attended severe disease and hospital admissions alongside overall infection rates."

Professor Yoon concluded by emphasizing, "Given that Enflonsia demonstrated efficacy in reducing RSV-related lower respiratory infections as well as hospitalizations, the evidence demonstrates the clinical value of this drug as an essential preventive option capable of alleviating the overall disease burden for infants entering their first RSV season."