RSV market competition intensifies in Korea

Arexvy expands adult indication….will compete with Moderna

Long-acting antibody injections go head-to-head…maternal immunization vaccine also near launch

The respiratory syncytial virus (RSV) prevention market is rapidly expanding across both adult and infant populations. In adults, GSK and Moderna are competing with vaccines, while in infants, Sanofi and MSD are competing with long-acting preventive antibody injections, with Pfizer’s maternal immunization vaccine also expected to enter the market.

With RSV prevention options becoming more diverse, calls are growing for financial support through inclusion in the National Immunization Program (NIP) or National Health Insurance reimbursement to enable broader market uptake. In particular, because preventive antibody injections for infants are medicines rather than vaccines, policymakers still need to determine whether their access should be expanded through the NIP or health insurance reimbursement.

According to industry sources on the 29th, competition is rapidly taking shape in Korea’s RSV prevention market, especially around adult vaccines and preventive antibody injections for infants.

In the adult market, GSK’s Arexvy is competing with Moderna’s mRESVIA. In the infant market, MSD Korea’s Enflonsia (clesrovimab) has received domestic authorization following Sanofi’s Beyfortus (nirsevimab). Pfizer’s RSV vaccine for pregnant women, Abrysvo, is also reportedly nearing approval in Korea.

RSV generally causes mild cold-like symptoms, but in infants, older adults, and patients with chronic diseases, it can progress to lower respiratory tract diseases such as bronchiolitis or pneumonia. Infants entering their first RSV season are particularly vulnerable because their immune systems are not fully developed and their airways are narrow, increasing the risk of severe disease and hospitalization.

A study analyzing Korean National Health Insurance claims data found that as many as 18,434 RSV cases occurred annually among children under five from 2007 to 2019, and 44.7% of all patients were hospitalized.

Infants aged 6 to 11 months accounted for 48.2% of RSV hospitalizations and 57.3% of intensive care unit admissions. Patients under 6 months had the longest average hospitalized days at 8.35 days, indicating a burden not only on infant health but also on caregiver responsibilities and healthcare resources.

Indication for GSK’s Arexvy expands to high-risk adults…builds long-term protection evidence

GSK’s Arexvy, Moderna’s mRESVIA

In the adult RSV vaccine market, the expansion of Arexvy’s indication is expected to reshape the competitive landscape.

GSK recently expanded the indication for Arexvy to high-risk adults aged 18 to 49. In addition to adults aged 60 and older and high-risk adults aged 50 to 59, the vaccine now covers adults aged 18 and older at increased risk of severe RSV due to chronic respiratory disease, cardiovascular disease, diabetes, chronic kidney disease, or immunocompromising conditions.

The expanded indication was based on a global Phase IIIb trial in high-risk adults aged 18 to 49. The study compared immune responses in this population with those in adults aged 60 and older and demonstrated non-inferiority. The safety profile was also comparable to that observed in previously vaccinated groups.

Arexvy has also generated evidence of efficacy and long-term protection in older adults. In the Phase III AReSVi-006 trial, its efficacy against RSV-associated lower respiratory tract disease during the first RSV season was 82.6% among adults aged 60 and older. The prevention effect was 94.6% among adults with at least one underlying condition.

Long-term follow-up showed cumulative efficacy of 62.9% over three RSV seasons after a single dose, while efficacy against severe RSV-associated lower respiratory tract disease was 67.4%. Although efficacy declined over time, the vaccine demonstrated protection across 3 seasons without a booster dose.

Moderna entered the competition with mRESVIA, which uses an mRNA platform. The vaccine is designed to produce the RSV F protein and is differentiated by extending the mRNA platform technology accumulated through COVID-19 vaccines to RSV prevention.

In Korea, mRESVIA is approved for preventing RSV-associated lower respiratory tract disease in adults aged 60 and older. Whether the indication will be expanded beyond older adults to younger high-risk groups, such as chronic disease and immunocompromised patients, is expected to be a key variable in the adult market.

Sanofi and MSD compete with preventive antibody injections…highlights reductions in hospitalization and severe disease

In the infant market, long-acting monoclonal antibodies formed the competitive landscape rather than vaccines.

Sanofi’s Beyfortus is a preventive antibody injection that directly administers antibodies to newborns and infants entering their first RSV season, providing protection immediately after infection. A single dose is designed to maintain protection for approximately 5 months.

RSV preventive antibody injections Beyfortus, Enflonsia

Beyfortus can be used not only in infants during their first RSV season but also in children under 24 months who remain at high risk of severe disease during their second season. The dose during the first season varies according to body weight, while a separate dose is used for high-risk children during the second season.

MSD Korea entered the infant RSV preventive antibody market after receiving domestic approval for Enflonsia in June.

Enflonsia is approved to prevent RSV-associated lower respiratory tract disease in newborns and infants entering their first RSV season or born during the season. It can be administered once at a fixed dose of 105 mg regardless of body weight, with protection lasting for at least 5-6 months.

The global Phase IIb/III CLEVER trial supporting approval enrolled approximately 3,600 healthy preterm and full-term infants born at 29 weeks of gestation or later across 22 countries, including Korea.

The study showed that Enflonsia reduced the risk of medically attended RSV-associated lower respiratory tract infection by 60.4% versus placebo through 150 days after administration. During the same period, it reduced the risk of RSV-related hospitalization by 84.2%. Through 180 days, it lowered the risk of medically attended severe RSV-associated lower respiratory tract infection by 91.7%.

In the safety analysis, more than 96% of reported adverse events were mild or moderate.

In the Phase III SMART trial involving preterm infants and infants with chronic lung disease or congenital heart disease who were at high risk of severe RSV, Enflonsia showed a generally similar safety profile to the established preventive antibody injection Synagis (palivizumab).

Enflonsia’s fixed-dose regimen is expected to simplify administration in clinical practice as there is no need to calculate the dose based on body weight or prepare different product presentations; it may improve convenience at healthcare institutions treating infants of varying birth dates, lunar ages and weights.

MSD Korea is also seeking to expand Enflonsia’s indication beyond the first RSV season to include children at high risk of severe disease during their second season.

The company has obtained follow-up data from the Phase III SMART trial in children under 2 years of age who remained at high risk across two RSV seasons. Among children given Enflonsia during their second season, blood drug concentrations were similar to those observed in healthy infants during their first season, while the safety profile remained consistent with earlier results.

If the indication is expanded to high-risk infants in their second season, the scope of competition with Beyfortus, which already holds that indication, is also expected to widen.

Pfizer’s Abrysvo nears approval… adding maternal immunization strategy

RSV vaccine Abrysvo

Pfizer is preparing to enter the infant RSV prevention market with a maternal immunization strategy that differs from those of preventive antibody injections.

Abrysvo is administered to pregnant women so that antibodies generated by vaccination are transferred to the fetus through the placenta. Unlike preventive antibody injections administered directly to infants after birth, the vaccine is designed to provide passive immunity against RSV from birth through vaccination during pregnancy.

In the US, Abrysvo was approved in 2023 for administration to pregnant women at 32 to 36 weeks of gestation to prevent RSV-associated lower respiratory tract disease and severe lower respiratory tract disease in infants through six months of age. It was the first vaccine approved to prevent RSV in infants through maternal immunization.

In the Phase III MATISSE trial supporting approval, vaccination during pregnancy reduced the risk of severe RSV-associated lower respiratory tract disease in infants by 81.8% through 90 days after birth. Efficacy through 180 days was 69.4%.

Abrysvo is also expected to receive approval in Korea soon. Once approved, infant RSV prevention will be divided between direct administration of a long-acting antibody after birth and transfer of antibodies before birth through maternal vaccination.

Because the 2 strategies differ in their target populations and timing of administration, they are likely to be selected based on maternal vaccination status, the infant’s birth timing, underlying conditions and risk of severe disease rather than serving as complete substitutes.

Prevention options become available… NIP and insurance coverage remain market variables

As RSV prevention products become available across adult and infant populations, attention is shifting to their funding mechanisms.

Given Korea’s transition to a super-aged society and the burden of hospitalization and mortality among older adults, the possible inclusion of RSV vaccines for older adults in the NIP may eventually be discussed. However, additional policy evidence is needed regarding the domestic disease burden, cost-effectiveness, and priority vaccination groups.

The framework for preventive antibody injections in infants is more complex. Beyfortus and Enflonsia are used to prevent infection but are monoclonal antibodies rather than vaccines. Policymakers must therefore determine whether they should be included in the NIP for government purchase and supply or covered through health insurance and prescribed by healthcare institutions.

The US Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices recommends long-acting preventive antibody injections for infants under 8 months who are entering or are already in their first RSV season. Overseas, preventive antibodies are increasingly being incorporated into public health prevention strategies.

At a press conference held on the 28th to mark Enflonsia’s approval, MSD Korea also emphasized the need to secure access through either NIP inclusion or health insurance coverage.

Discussions on institutional access in Korea’s RSV prevention market may therefore initially progress more rapidly in the infant segment. The government has historically prioritized the pediatric NIP over vaccination programs for older adults.

With the hospitalization and severe disease burden of RSV in infants already established and multiple products demonstrating preventive efficacy, calls for financial support are increasing. Sanofi and MSD are exploring potential NIP inclusion or health insurance coverage for their preventive antibodies. Once Prizer receives approval for Abrysvo in Korea, policy discussions on infant RSV prevention are expected to broaden to include maternal immunization.