MSD-Boryung signs copromotion agreement for Enflonsia

May rise as a competitor to Sanofi’s Beyfortus… armed with the convenience of a 'single-dose administration regardless of body weight’

Co-promotion will launch in July…signaling market entry ahead of the RSV season in the second half of the year.

MSD Korea has partnered with Boryung Biopharma to commercialize Enflonsia (clesrovimab), its monoclonal antibody for the prevention of respiratory syncytial virus (RSV) in neonates and infants.

According to industry sources, on July 1 the two companies signed a strategic partnership agreement covering domestic distribution and co-promotion of Enflonsia in Korea. Under the agreement, Boryung Biopharma will begin handling domestic distribution and joint promotional activities targeting healthcare professionals starting July 1.

Enflonsia is a long-acting monoclonal antibody that provides at least 5-6 months of protection following a single dose in neonates and infants. In the large-scale global Phase III CLEVER trial, the therapy demonstrated clinical efficacy, reducing RSV-related hospitalizations by 84.2%.

Expectations are rising on site on the convenience of administration of Enflonsia. Compared with Beyfortus, which has already established a presence in the market, Enflonsia offers a simpler dosing regimen. Beyfortus requires different dosage strengths depending on an infant's body weight (5 kg) as the dosing threshold. In contrast, Enflonsia is administered as a single fixed dose regardless of body weight.

The infant RSV prevention market in Korea is currently led by Sanofi and SK Bioscience. To strengthen its market position, MSD Korea selected Boryung Biopharma as its commercialization partner, citing the company's extensive distribution network and long-standing expertise in vaccine and pharmaceutical sales, particularly in primary care clinics.

The upcoming RSV season in the second half of the year is expected to be the first major commercial opportunity for Enflonsia. In Korea, the RSV season typically runs from October through March. Infants born during the RSV season are expected to receive a single dose shortly after birth, while those born outside the season are scheduled to receive one dose before the start of their first RSV season. The two companies plan to rapidly expand the product's market presence in line with this schedule.

Although RSV infection typically begins with symptoms resembling those of the common cold, it can progress to lower respiratory tract infections, including bronchiolitis and pneumonia, in infants younger than one year of age, often requiring hospitalization.

According to a nationwide study based on National Health Insurance claims data covering 2007 to 2019, published last year, 44.7% of Korean children younger than five years diagnosed with RSV required hospitalization. In particular, infants aged 6 to 11 months accounted for approximately 48.2% of RSV-related hospitalizations and 57.3% of intensive care unit (ICU) admissions among children under five, representing the highest hospitalization burden. Infants younger than six months had the longest average hospital stay, at 8.35 days.

Enflonsia received marketing authorization in Korea on July 1. The approval was supported by results from the global Phase IIb/III CLEVER trial and the Phase III SMART study.

The CLEVER study evaluated approximately 3,600 healthy newborns and infants born at 29 weeks' gestation or later across 22 countries and demonstrated a 60.4% reduction versus placebo in the primary endpoint of medically attended lower respiratory tract infection (MALRI) associated with RSV.

In the safety analysis, more than 96% of adverse events reported with Enflonsia were mild or moderate in severity. The Phase III SMART study, which enrolled premature infants and infants at high risk for severe RSV disease, including those with chronic lung disease (CLD) or congenital heart disease (CHD), also demonstrated an overall safety profile comparable to that of the control treatment (palivizumab).