Adjuvants have several important benefits.
Reducing the Amount of Antigen Required
Adding an adjuvant can reduce the amount of antigen, or pathogen component, required in a vaccine to elicit a protective immune response. The ability to increase the number of vaccine doses that can be produced for public use may be especially important during an epidemic or pandemic. For example, the U.S. stockpiled pandemic influenza vaccine contains four times less antigen than the standard influenza vaccine because it is formulated with an adjuvant (see Adjuvants Used in U.S. Vaccines).
Reducing the Number of Vaccine Doses Needed
A person may need fewer doses of a vaccine containing a certain adjuvant because the immune response may be more effective. For example, results from clinical trials indicate that two doses of an investigational hepatitis B vaccine containing a novel adjuvant given over one month elicit potent, long-lasting protection. The current hepatitis B vaccine, which contains alum, requires three doses over six months. In addition, for a small number of people, the current vaccine does not confer immunity against the hepatitis B virus. Research suggests that the investigational vaccine is effective for almost everyone.
Enhancing Vaccine Effectiveness in Immunocompromised People
People with compromised immune systems, such as the elderly or the very young, may benefit from vaccines with adjuvants because their immune systems may require an extra boost to provide protection. A good example of this is the vaccine against herpes zoster (shingles), a condition that affects many elderly people. Shingles is caused by the same virus that causes chickenpox. After a person recovers from chickenpox, the virus goes into hiding in nerve cells and can be reactivated when the immune system is weakened, such as by aging. The shingles vaccine Zostavax, which contains a weakened chickenpox virus, decreases the risk of disease by half in people between the ages of 50 and 80. However, older vaccine recipients are not as well protected by the vaccine. In contrast, a new experimental shingles vaccine being developed by the pharmaceutical company GlaxoSmithKline that consists of only one viral protein and a novel adjuvant (AS01) protects almost all recipients from the disease, regardless of age. This vaccine is also beneficial for other groups at risk of shingles, such as cancer patients receiving certain treatments.
Additionally, a European study showed that addition of MF59 adjuvant to a seasonal influenza vaccine boosted the vaccine’s effectiveness in young children from 43 percent to 89 percent.
Boosting the Immune-Stimulating Effects of Vaccines
Adjuvants are especially effective at boosting the immune-stimulating effects of newer vaccines, such as those made with purified antigens. By enhancing immune responses to pathogen antigens, adjuvants may help scientists develop vaccines against infectious diseases for which no effective vaccine currently exists, such as tuberculosis or HIV/AIDS.
Offering Broad Protection
Adjuvanted vaccines may offer broad protection against related strains (types) of pathogens. For example, the human papillomavirus (HPV) vaccine Cervarix, which contains the AS04 adjuvant, is designed to prevent infection by HPV 16 and 18, the two strains that cause approximately 70 percent of cervical cancers in more than half a million women worldwide every year. Results from clinical trials show that Cervarix protects against two additional cancer-causing strains, HPV 45 and 31. The use of AS04 in this vaccine also increases the level of protection the vaccine provides.
Directing Specific Immune Responses
Adjuvants can direct specific immune responses to provide protection against the pathogen that the vaccine targets. Bacteria, viruses, and parasites use different infection strategies, and therefore, each is thwarted by different components of the immune system. Certain adjuvants may be more effective at stimulating responses to a particular vaccine antigen. Vaccine developers must tailor each antigen-adjuvant combination to maximize the safety and effectiveness of a vaccine. The availability of a toolbox of adjuvants would help scientists direct the different immune responses required against the many pathogens that cause disease. Therefore, to aid the development of new and improved vaccines, researchers are working to identify novel adjuvants and adjuvant-antigen combinations.
Like any medication, vaccines and adjuvants can cause side effects. The most common side effects of vaccines are mild and include redness or swelling at the injection site. In very rare cases, vaccines may cause severe side effects such as allergic reactions. Identifying vaccine formulations that are safe as well as effective is a major focus of vaccine and adjuvant development research supported by NIAID.
It is important to keep in mind, however, that the benefits of vaccines far outweigh the potential risks. Vaccines have greatly reduced the occurrence of many life-threatening diseases. For example, before the introduction of the measles vaccine, this disease affected over 500,000 people each year in the United States. According to the Centers for Disease Control and Prevention, an estimated 200 people were diagnosed with the disease in 2013. This is a 96 percent decrease from pre-vaccination levels, and most of those infected in 2013 were unvaccinated.
Read more about Vaccine Benefits.