GSK strikes $3.3B Affinivax buyout to MAP out challenge to Pfizer's blockbuster pneumococcal vaccine

GSK is betting big to reenergize its fight for a share of the pneumococcal vaccine market, agreeing to pay $2.1 billion upfront to acquire Affinivax for a challenger to Pfizer’s blockbuster Prevnar franchise.

The British Big Pharma already has an approved pneumococcal vaccine, Synflorix, but has failed to turn it into a true rival to Pfizer’s incumbent. Sales of Synflorix fell (PDF) to 357 million pounds sterling ($450 million) last year, while the Prevnar range of vaccines still topped (PDF) $5 billion in the face of COVID-related headwinds and the timing of government purchases. Last year’s approval of Merck & Co.'s Vaxneuvance further intensified competition. 

GSK has responded by inking a deal to buy privately held Affinivax for $2.1 billion upfront and two $600 million milestones tied to pediatric clinical development. The takeover will give GSK full control of a 24-valent pneumococcal vaccine candidate that Affinivax plans to move into phase 3 in older adults and phase 1/2 trials in children this year. The Merck and Pfizer vaccines that won approval last year protect against 15 and 20 strains of pneumococcal serotypes, respectively.

Boston-based Affinivax established its candidate, AFX3772, as a potential challenger last year when it reported data from a phase 2 trial that enrolled 503 adults aged 65 to 85 years. The study linked the vaccine to higher immune responses to certain serotypes than were achieved by Pfizer’s last-generation Prevnar 13, with or without a shot of Merck’s Pneumovax 23. 

Pfizer has since brought Prevnar 20 to market, reducing the advantage AFX3772 has in terms of serotype coverage. Yet, Affinivax’s pitch is about more than just the number of serotypes. The biotech, which paid Astellas $65 million to regain rights to AFX3772 in February, also argues its multiple antigen-presenting system, MAPS, induces a broader protective immune response than conventional conjugate vaccine technologies.

Access to the platform, which is designed to induce B-cell and T-cell responses, is part of the appeal of the deal for GSK, as the company’s chief scientific officer Hal Barron, M.D., explained in a statement. 

“The proposed acquisition further strengthens our vaccines R&D pipeline, provides access to a new, potentially disruptive technology and broadens GSK’s existing scientific footprint in the Boston area,” Barron said.

GSK’s move for Affinivax comes six weeks after it struck a deal to buy Sierra Oncology for $1.9 billion. The back-to-back deals, which are worth $4 billion upfront between them, mark a busy end to Barron’s time at GSK. The executive is set to leave the company later this year to become CEO of Altos Labs.