What Are the Names of Adjuvants: A Comprehensive Guide

October 10, 2025 •

5 min read

Over 70 years of vaccine history has proven the safety and effectiveness of adjuvants like aluminum salts. A deep dive into what are the names of adjuvants reveals a diverse landscape, ranging from simple mineral carriers to complex immunomodulatory systems used in modern medicine.

Quick Summary

Adjuvants are substances that boost the immune response to a vaccine's antigen. They include mineral salts like alum, oil-in-water emulsions such as MF59 and AS03, and TLR agonists like CpG 1018. Newer systems like AS01 and Matrix-M combine different components for enhanced effects.

Key Points

Aluminum salts (Alum): The most widely used adjuvants in licensed vaccines for decades, including aluminum hydroxide and aluminum phosphate, which function as antigen depots.
Oil-in-water emulsions (MF59, AS03): Squalene-based adjuvants used in influenza vaccines to enhance immune responses, particularly in older adults and children.
Toll-like receptor (TLR) agonists (MPLA, CpG): Molecules that mimic components of pathogens to activate innate immunity. MPL is a TLR4 agonist, while CpG oligonucleotides activate TLR9.
Combined adjuvant systems (AS01, AS04): Advanced adjuvants combining a delivery system (e.g., aluminum salts or liposomes) with an immunomodulator (e.g., MPL or QS-21) for a synergistic effect.
Saponin-based adjuvants (QS-21, Matrix-M): Extracts from the Quillaja saponaria tree that induce both humoral and cellular immune responses. QS-21 is in AS01, while Matrix-M is in some COVID-19 and malaria vaccines.
Adjuvants in immunotherapy: In addition to traditional vaccines, adjuvants like microcrystalline tyrosine and TLR agonists are utilized in allergen and cancer immunotherapies to modulate specific immune responses.

An adjuvant is a key ingredient added to some vaccines and immunotherapies to enhance and shape the body's immune response to an antigen. Many modern vaccines, especially those containing inactivated or subunit antigens, would produce a weak or insufficient immune reaction without an adjuvant. Adjuvants work by a variety of mechanisms, such as creating a 'depot effect' to prolong antigen presence at the injection site or by activating innate immune cells to amplify the response. The selection of an adjuvant is a careful process, depending on the vaccine type, the desired immune pathway (e.g., T-helper type 1 vs. type 2), and the target population.

Common Adjuvant Categories and Names

Mineral Salts

Mineral salts are the oldest and most widely used adjuvants, with aluminum salts being approved for human vaccines since the 1930s. They function primarily as a delivery system by adsorbing antigens to their surface, creating a deposit that slows the release of the antigen and prolongs its exposure to the immune system. This enhances the production of antibodies, particularly of the Th2 type.

Aluminum salts: A general term referring to several aluminum-based compounds.
Aluminum hydroxide: Used in many vaccines, including those for anthrax, hepatitis A, hepatitis B, and various combination vaccines. A commercial example for research is Alhydrogel.
Aluminum phosphate: Another widely used aluminum-based adjuvant, found in vaccines for diphtheria-tetanus-acellular pertussis (DTaP) and pneumococcal disease. A trade name for research is Adju-Phos.
Amorphous aluminum hydroxyphosphate sulfate (AAHS): A variation of aluminum salt used in vaccines like Gardasil 9 for HPV and some hepatitis B vaccines.
Calcium phosphate: A less common mineral salt adjuvant, sometimes used in vaccines for diphtheria-tetanus (DT).

Oil-in-Water Emulsions

These adjuvants consist of small droplets of oil dispersed in a watery solution, which create an antigen depot and stimulate a localized inflammatory response.

MF59: Composed of squalene (an oil), Tween 80, and Span 85, this adjuvant is used in certain influenza vaccines (e.g., Fluad) for individuals aged 65 or older.
AS03: Another squalene-based emulsion containing alpha-tocopherol (Vitamin E) and polysorbate 80. It was used in pandemic influenza vaccines.
Freund's Adjuvant: A historical adjuvant, typically used in animal studies, with two forms: Complete Freund's Adjuvant (CFA), which contains heat-killed Mycobacterium, and Incomplete Freund's Adjuvant (IFA) without the mycobacteria.

Toll-Like Receptor (TLR) Agonists

TLRs are receptors on immune cells that recognize pathogen-associated molecular patterns (PAMPs). Agonists are synthetic or derived substances that activate these receptors to stimulate a potent immune response, particularly favoring the Th1 pathway.

Monophosphoryl lipid A (MPLA): A detoxified form of bacterial lipopolysaccharide (LPS) that activates TLR4. It is a component of several advanced adjuvants, including AS01 and AS04.
CpG 1018: Synthetic DNA sequences that mimic bacterial DNA and activate TLR9. This adjuvant is used in the hepatitis B vaccine Heplisav-B and some anthrax vaccines.
QS-21: A purified saponin from the bark of the Quillaja saponaria tree. It activates the inflammasome and is a key component of the AS01 adjuvant system.
Poly(I:C): A synthetic double-stranded RNA molecule that activates TLR3.

Combined Adjuvant Systems

Complex adjuvants combine multiple components to harness different mechanisms of action, aiming for a stronger or more balanced immune response.

AS01: A liposomal formulation combining MPL (TLR4 agonist) and QS-21 (saponin). It is used in the recombinant shingles vaccine, Shingrix.
AS04: Contains MPL (TLR4 agonist) adsorbed onto an aluminum salt. It is or was used in the HPV vaccine Cervarix and a hepatitis B vaccine.
Matrix-M: A saponin-based adjuvant system (containing QS-21, cholesterol, and phospholipids) used in the Novavax COVID-19 vaccine.

Other Adjuvant Systems

Liposomes: Lipid-based vesicles that encapsulate and deliver antigens, sometimes containing other immunomodulators.
Virosomes: Empty viral envelope structures that present antigens, mimicking viruses to enhance the immune response.
Microcrystalline tyrosine (MCT): A depot adjuvant used in allergen-specific immunotherapy that slows allergen release.
Cytokines: Immune system signaling proteins, such as GM-CSF (granulocyte-macrophage colony-stimulating factor), used to stimulate and recruit immune cells.

Comparison of Adjuvants


Adjuvant Type	Specific Name(s)	Composition	Examples of Use	Primary Mechanism(s)
Mineral Salts	Aluminum hydroxide, Aluminum phosphate	Aluminum salts	DTaP, Hepatitis B, HPV (Gardasil)	Antigen depot, NLRP3 inflammasome activation
Emulsions	MF59, AS03	Squalene, surfactants	Seasonal and pandemic influenza	Antigen depot, cytokine/chemokine induction
Combined System	AS04	MPL + aluminum salt	HPV (Cervarix), Hepatitis B (Fendrix)	Depot effect, TLR4 activation
Combined System	AS01B	MPL + QS-21 (in liposomes)	Recombinant zoster (Shingrix)	TLR4 activation, inflammasome activation
TLR Agonist	CpG 1018	Synthetic DNA (CpG motifs)	Hepatitis B (Heplisav-B)	TLR9 immune stimulation
Saponin-based	Matrix-M™	Saponins (QS-21), cholesterol, phospholipids	COVID-19 (Novavax)	Humoral and cellular immune stimulation
Delivery System	Liposomes, Virosomes	Lipid vesicles or viral envelopes	Hepatitis, Influenza	Encapsulation, delivery to cells

The Role of Adjuvants in Different Therapies

Adjuvants are not limited to traditional infectious disease vaccines. They are increasingly used in other areas of medicine to modulate immune responses in specific ways.

Allergen-Specific Immunotherapy (AIT): Adjuvants are used to shift the immune response away from an allergic (Th2) pathway toward a more tolerant (Th1) or regulatory T-cell response. Microcrystalline tyrosine (MCT) is a depot adjuvant used in AIT to slow allergen release and reduce systemic side effects. The use of bacterial derivatives like MPL is also explored for their Th1-promoting effects.
Cancer Vaccines: Adjuvants for cancer vaccines must provoke a strong cell-mediated (Th1 and CD8+ T cell) immune response to target and eliminate tumor cells. In addition to TLR agonists like MPLA and CpG-ODN, other molecules like STING agonists are being investigated for their potent type-I interferon response. Nanoparticle-based adjuvants are also being developed to efficiently deliver antigens to antigen-presenting cells (APCs).

Conclusion

Adjuvants are a diverse class of pharmacological agents critical for maximizing the effectiveness of many vaccines and immunotherapies. From the decades-long use of simple aluminum salts to the development of sophisticated multi-component systems like AS01 and AS04, the field of adjuvants continues to evolve. The growing understanding of immune mechanisms has led to the rational design of adjuvants that can be specifically tailored to the antigen, administration route, and desired immune outcome. While traditionally used in vaccines for infectious diseases, modern adjuvants are now integral to therapeutic strategies for allergies and cancer, underscoring their vital role in shaping protective immunity in modern medicine.

Frequently Asked Questions

The primary function of an adjuvant is to boost the body's immune response to an antigen in a vaccine. This is especially important for vaccines made from weakened or inactive antigens, which would otherwise not provoke a strong immune reaction on their own.

Aluminum salts, including aluminum hydroxide, aluminum phosphate, and amorphous aluminum hydroxyphosphate sulfate, are the most commonly used adjuvants in licensed human vaccines and have been used for over 70 years.

Yes, adjuvants can be broadly classified as delivery systems (like aluminum salts, oil emulsions, and liposomes) that create an antigen depot, and immunomodulators (like TLR agonists) that directly stimulate immune cells.

Examples include AS01, a liposomal formulation with MPL and QS-21 used in the Shingrix vaccine, and AS04, which combines MPL with an aluminum salt. Matrix-M, a saponin-based system, is another example used in newer vaccines.

CpG oligonucleotides (e.g., CpG 1018) are synthetic DNA sequences that mimic bacterial DNA and activate Toll-like receptor 9 (TLR9) on immune cells. This stimulates a strong Th1-type immune response.

The choice of adjuvant depends on the type of immune response required for protection against a specific pathogen. Some adjuvants favor a strong antibody response, while others are better at stimulating a cellular (T-cell) response.

For allergen-specific immunotherapy (AIT), adjuvants include aluminum hydroxide, calcium phosphate, and microcrystalline tyrosine. Newer strategies also explore immunomodulators like MPL and CpG motifs to steer the immune response toward tolerance.