Adjuvants help vaccines work better.

What is an adjuvant and why is it added to a vaccine?

vaccine vials

An adjuvant is an ingredient used in some vaccines that helps create a stronger immune response in people receiving the vaccine. In other words, adjuvants help vaccines work better. Some vaccines that are made from weakened or killed germs contain naturally occurring adjuvants and help the body produce a strong protective immune response. However, most vaccines developed today include just small components of germs, such as their proteins, rather than the entire virus or bacteria. Adjuvants help the body to produce an immune response strong enough to protect the person from the disease he or she is being vaccinated against. Adjuvanted vaccines can cause more local reactions (such as redness, swelling, and pain at the injection site) and more systemic reactions (such as fever, chills and body aches) than non-adjuvanted vaccines.

Adjuvants have been used safely in vaccines for decades.

Aluminum salts, such as aluminum hydroxide, aluminum phosphate, and aluminum potassium sulfate have been used safely in vaccines for more than 70 years. Aluminum salts were initially used in the 1930s, 1940s, and 1950s with diphtheria and tetanus vaccines after it was found they strengthened the body’s immune response to these vaccines.

Newer adjuvants have been developed to target specific components of the body’s immune response, so that protection against disease is stronger and lasts longer.

In all cases, vaccines containing adjuvants are tested for safety and effectiveness in clinical trials before they are licensed for use in the United States, and they are continuously monitored by CDC and FDA once they are approved.

Several different adjuvants are used in U.S. vaccines.

Several different adjuvants are used in U.S. vaccines.
Adjuvant Composition Vaccines
Aluminum One or more of the following: amorphous aluminum hydroxyphosphate sulfate (AAHS), aluminum hydroxide, aluminum phosphate,
potassium aluminum sulfate (Alum)
Anthrax, DT, DTaP (Daptacel), DTaP (Infanrix), DTaP-IPV (Kinrix), DTaP-IPV (Quadracel), DTaP-HepB-IPV (Pediarix), DTaP –IPV/Hib (Pentacel), Hep A (Havrix), Hep A (Vaqta), Hep B (Engerix-B), Hep B (Recombivax), HepA/Hep B (Twinrix), HIB (PedvaxHIB), HPV (Gardasil 9), Japanese encephalitis (Ixiaro), MenB (Bexsero, Trumenba), Pneumococcal (Prevnar 13), Td (Tenivac), Td (Mass Biologics), Tdap (Adacel), Tdap (Boostrix)
AS04 Monophosphoryl lipid A (MPL) + aluminum salt Cervarix
MF59 Oil in water emulsion composed of squalene Fluad
AS01B Monophosphoryl lipid A (MPL) and QS-21, a natural compound extracted from the Chilean soapbark tree, combined in a liposomal formulation Shingrix
CpG 1018 Cytosine phosphoguanine (CpG), a synthetic form of DNA that mimics bacterial and viral genetic material Heplisav-B
No adjuvant ActHIB, chickenpox, live zoster (Zostavax), measles, mumps & rubella (MMR), meningococcal (Menactra, Menveo), rotavirus, seasonal influenza (except Fluad), single antigen polio (IPOL), yellow fever

Aluminum-containing adjuvants are vaccine ingredients that have been used in vaccines since the 1930s. Small amounts of aluminum are added to help the body build stronger immunity against the germ in the vaccine. Aluminum is one of the most common metals found in nature and is present in air, food, and water. Scientific research has shown the amount of aluminum exposure in people who follow the recommended vaccine schedule is low and is not readily absorbed by the body. Read the research on aluminum exposure and vaccines.External  Also, see FDA’s web page on common ingredients in U.S. licensed vaccinesExternal for more information.

Beginning in 2009, monophosphoryl lipid A (MPL) was used in one U.S. vaccine (Cervarix®); however, the vaccine is no longer available in the United States due to low market demand. This immune-boosting substance was isolated from the surface of bacteria.

MF59 is the adjuvant contained in Fluad (an influenza vaccine licensed for adults aged 65 or older). MF59 is an oil-in-water emulsion composed of squalene, which is a naturally occurring oil found in many plant and animal cells, as well as in humans. MF59, used in flu vaccines in Europe since 1997 and in the United States since 2016, has been given to millions of people and has an excellent safety record.

AS01B is an adjuvant suspension used with the antigen component of Shingrix vaccine. Shingrix is the recombinant zoster vaccine recommended for persons aged 50 years or older. AS01B is made of up of monophosphoryl lipid A (MPL), an immune-boosting substance isolated from the surface of bacteria, and QS-21, a natural compound extracted from the Chilean soapbark tree (Quillaja saponaria Molina). In pre-licensure clinical trials, AS01B was associated with local and systemic reactions, but the overall safety profile was reassuring.

AS01B is also a component of vaccines currently being tested in clinical trials, including malaria and HIV vaccines. To date, these trials have included over 15,000 people.

CpG 1018
CpG 1018 is a recently developed adjuvant used in Heplisav-B vaccine. It is made up of cytosine phosphoguanine (CpG) motifs, which is a synthetic form of DNA that mimics bacterial and viral genetic material. When CpG 1018is included in a vaccine, it increases the body’s immune response.

In pre-licensure clinical trials, adverse events after Heplisav-B were comparable to those observed after another U.S.-licensed, non-adjuvanted hepatitis B vaccine.


CDC and FDA closely monitor the safety of all vaccines.

CDC and the Food and Drug Administration (FDA) are committed to ensuring that vaccines provided to the public are safe and effective.  Once vaccines are licensed in the United States, CDC and FDA continuously monitor them through several safety systems. Learn more about CDC’s vaccine safety systems.