[Edaily Reporter KIM SUNG-JIN ] With Baeksite successfully completing Phase 3 clinical trials for its pneumococcal vaccine “VAX-31” in adults, competition in the pneumococcal vaccine market appears to be intensifying. The vaccine for which BackSite has now successfully completed clinical trials is designed to prevent as many as 31 pneumococcal serotypes. This means that the 31-valent vaccine has cleared the Phase 3 clinical trial hurdle even before the 21-valent pneumococcal vaccine “GBP410”—which SK BIOSCIENCE(302440)is jointly developing with Sanofi—has been launched.

Since BackSite is developing a vaccine for adults and SK BIOSCIENCE is developing one for children and infants, it does not appear that a direct competitive dynamic will form immediately. However, as both companies are expanding their development scope to include infants and adults, respectively, competition is expected to broaden to all age groups in the future.

Global Market Dominated by Pfizer and Merck… Attention on VAX-31 Clinical Results

According to recent industry reports, U.S. vaccine developer BackSite recently announced positive results from the Phase 3 clinical trial of VAX-31, a pneumococcal protein-conjugate vaccine (PCV) candidate. Although pneumococcus is a single bacterium, it is divided into multiple serotypes based on its surface structure. A 31-valent vaccine refers to a vaccine capable of preventing all 31 serotypes. BackSite estimates that this 31-valent vaccine could prevent approximately 88% of pneumococcal pneumonia cases.

Industry observers view the success of Bacsight’s Phase 3 clinical trial for the 31-valent pneumococcal vaccine as highly significant. Since the existing vaccine market is oligopolized by a few global pharmaceutical giants—such as Merck, Pfizer, GSK, and Sanofi—there has long been a call for new entrants to the market.

In fact, according to the “Global Vaccine Market Report 2025” published by the World Health Organization (WHO), Merck accounted for 21% of the total market by revenue, followed by Pfizer at 20% and GSK at 17%. Sanofi also accounted for 13% of sales, bringing the total share held by these four companies to over 70% of total revenue.

When narrowing the focus to the pneumococcal vaccine market, this oligopolistic structure becomes even more evident. According to documents submitted by BackSite to the U.S. Securities and Exchange Commission (SEC), Pfizer’s revenue share in the pneumococcal vaccine market as of 2025 was 77%, while Merck’s was 21%. In effect, these two companies dominate the market.

Against this backdrop, the market reacted enthusiastically when BackSite successfully completed Phase 3 clinical trials for its 31-valent vaccine. On the 5th (local time), when news of the Phase 3 success broke, BackSite’s stock price closed at $73.82, up 30.7% from the previous trading day. Although the stock price subsequently dipped to $65, it rebounded by 9.79% on the 9th, regaining the $70 mark. Considering that the stock price had hovered around the $50 mark prior to the announcement of the clinical results, analysts note that it remains at a relatively high level.

Backsite plans to announce the results of the remaining two Phase 3 trials in adults (OPUS-2 and OPUS-3) in the first half of next year. OPUS-2 evaluates the safety and immunogenicity of VAX-31 when administered concurrently with the seasonal flu vaccine, while OPUS-3 assesses the efficacy of VAX-31 in adults who have previously received the pneumococcal vaccine. The company aims to submit a Biologics License Application (BLA) to the U.S. Food and Drug Administration (FDA) in the first half of 2028 once the results of these two trials are available.

GBP410 Phase 3 Clinical Trial Underway… BackSite Also Expanding Clinical Trials for Infants and Toddlers

The results of BackSite’s adult clinical trials are also drawing attention to SK BIOSCIENCE, which is developing a pneumococcal vaccine in South Korea. SK BIOSCIENCE is jointly developing GBP410, a 21-valent pneumococcal protein-conjugate vaccine candidate, with Sanofi.

The collaboration between the two companies began in 2014. At that time, SKCHEMICALS signed a global joint development and marketing agreement with Sanofi Pasteur for a next-generation pneumococcal vaccine. Subsequently, GBP410 secured positive results in a Phase 2 clinical trial for infants and young children in June 2023 and is currently undergoing a Phase 3 clinical trial. SK BIOSCIENCE is preparing to announce interim results in 2027.

GBP410 is a vaccine candidate for infants and young children that targets 21 serotypes. The primary goal of its development is to broaden the scope of protection by covering more serotypes than existing vaccines. Of course, this does not mean that BackSite and SK BIOSCIENCE are currently competing in the same market. This is because the vaccine candidate for which BackSite has now successfully completed Phase 3 clinical trials is intended for adults, whereas SK BIOSCIENCE is conducting Phase 3 trials for infants and young children.

A key variable going forward is the pace of BackSite’s development for infants and young children. BackSite is also conducting a Phase 2 clinical trial of VAX-31 for this age group and plans to announce the results of the primary and booster doses by the first half of 2027. If it proceeds to subsequent clinical trials and continues development, the competition that began in the adult market could expand to the infant and toddler market. This can be interpreted to mean that it is becoming increasingly difficult to secure long-term competitiveness in the pneumococcal vaccine market based solely on the differentiation of “20 serotypes or more.”

However, some argue that a vaccine cannot be considered effective simply because it offers a broad range of protection. An industry official stated, “The key to commercialization lies in how broadly it can prevent serotypes that are actually circulating, whether safety and immunogenicity can be demonstrated, and whether sufficient efficacy is confirmed in age-specific clinical trials,” adding, “A high number of serotypes does not automatically prove clinical superiority.”

SK BIOSCIENCE is also pursuing the development of a vaccine with a broader scope of protection. SK BIOSCIENCE and Sanofi agreed in late 2024 to expand their existing collaboration to jointly develop a next-generation pneumococcal vaccine targeting infants, children, and adults. Their strategy is to broaden the scope of pneumococcal protection through a next-generation vaccine that includes more serotypes than GBP410.

An SK BIOSCIENCE official said, “It is true that we are entering a competitive landscape with Bacsite, but it will also be noticeable that prices tend to rise as the number of serotypes increases,” adding, “Since Bacsite has not yet released its final results, we will need to wait and see.”