Several combination adjuvants have been developed and are currently in use or under investigation. One notable example is the AS04 adjuvant system, which combines aluminum hydroxide with monophosphoryl lipid A (MPL). This combination is used in the human papillomavirus (HPV) vaccine to enhance both the humoral and cellular immune responses. Another example is MF59, an oil-in-water emulsion that includes squalene, which has been used in influenza vaccines to improve immunogenicity.
