Understanding adjuvant supply chains for new TB and malaria vaccines

In recent years, vaccine development has seen significant advances for the infectious diseases that cause the most deaths.

Over a century since the introduction of the only existing TB vaccine, BCG, multiple new vaccines could be approved in coming years. If approved, M72/AS01E, a leading candidate, could avert millions of deaths in India alone, by 2050 [1].

The first malaria vaccines, RTS,S/AS01E and R21/Matrix-M, were approved in 2015 and 2023, respectively. Both show approximately 75% effectiveness in preventing malaria episodes when given in areas of high transmission [2].

These three breakthrough vaccines share a key ingredient: saponin-based adjuvants, extracted from the quillay tree (Quillaja saponaria) that grows almost exclusively in mountainous forests in central Chile. Importantly, these saponin adjuvants are also used in widely distributed vaccines for RSV, shingles, HPV, and COVID-19. Because the adjuvant saponins are found in very low concentrations in quillay trees (with an extraction yield equivalent to 0.0032% by weight of biomass) [3], a large number of trees must be harvested annually. As these forests suffer droughts and forest fires, and quillay saponins are used in several other industries — including cosmetics, in beverages, and in animal feed — which may compete with adjuvants as more profitable uses. A lack of information on the supply chain and the supplies needed to assure vaccine manufacturing volumes has elicited concerns that the supply of quillay saponins could potentially create a bottleneck for vaccine manufacturing.