A Vital Adjuvant Ingredient - A Precious Natural Resource

JANUARY 2024

GSK’s malaria vaccine, Mosquirix®(RTS,S), is finally being administered in many African countries, where malaria is considered one of the biggest killers of young children, and where 95% of all fatal malaria cases occur. Mosquirix® is one of two malaria vaccines that are recommended by the World Health Organization (WHO). R21 is the second, developed by University of Oxford and manufactured by the Serum Institute of India. Both vaccines are expected to meet the growing demand for protection against malaria, which experts estimate will be 40-60 million doses per year by 2026.

The “secret sauce” of both the Mosquirix® and R21 vaccines, however, includes a key ingredient called QS-21, a saponin incorporated in adjuvant formulations for its immune-boosting properties.  QS21 provides an immune-stimulating boost to make vaccines effective against complex diseases like malaria. But QS-21 is derived from oil extracted from a rare Chilean Soapbark tree, Quillaja Saponaria, of which there is scarce supply and for which there are no effective alternatives.  The scarcity and expense of QS21 creates a significant barrier to vaccine access.

Malaria is not the only disease from which QS-21 helps provide protection. QS-21 is a key ingredient in GSK’s blockbuster shingles vaccine, Shingrix®, the new RSV vaccine, Arexvy®, and the leading new tuberculosis vaccine candidate that is entering late-stage clinical trials ("M72"). The high demand for QS-21 threatens vaccine supply and long-term availability of this critical vaccine ingredient. The vaccine industry is becoming increasingly reliant on supply of the Quillaja tree bark – with one major vaccine rollout requiring 5,000-7,000 trees per year.  

melind f. moree

thing global health

Sufficient supply of the adjuvant remained a question during the phase  3 trial despite many conversations with GSK to confirm the commitment. The supply of adjuvant is now the limiting factor for international rollouts. 

Improved access to adjuvants such as QS21 is critical to ensuring vaccine supply.  Scientists are working to reduce dependence on current sources of QS21. AAHI scientists innovated a high-yield, high-purity extraction process, to extract maximum yield of QS21, and continue to collaborate to identify and formulate more sustainably sourced saponins.  Scientists are exploring alternatives to tree bark – extracting QS21 precursors from renewable leaves, for example, as opposed to stripping tree bark.  Other scientists are using plant tissue culture to grow synthetic trees. And efforts continue to better understand the biomechanics of QS21’s immune-stimulating effects, bringing new perspectives to development of potential sustainable and scalable alternative sources of QS-21.

AAHI is committed to providing sustainable and accessible adjuvant formulations that will make vaccine roll outs reliable, effective, and impactful.  We develop and deploy adjuvants that are inexpensively synthesized from sustainable materials, stable at room temperature, and safely enhance immune responses against a wide variety of threats. We have one of the largest portfolios of adjuvants, and we work with dozens of vaccine developers and global stakeholders to make them available for vaccines for global health. Adjuvants no longer have to be the "limiting factor" that prevents the international rollout of lifesaving vaccines.