What are Adjuvants in Vaccines?

When you roll up your sleeve for a vaccine, you’re often getting more than just the active ingredient that helps protect against illness from an infection. Hidden in the mix of many vaccines is a key component, called an adjuvant, that helps strengthen your body’s defenses against disease-causing viruses and bacteria.

“Adjuvant” comes from a Latin word that means “to aid or support” — “and that’s exactly what the adjuvant does,” says Dr. William Schaffner, an infectious disease specialist and professor of medicine at the Vanderbilt University School of Medicine. “It’s an additional vaccine ingredient that helps stimulate the immune system so that the immune system responds better to the vaccine.”

In other words, Schaffner says, “it makes the vaccine more effective.”

Several common vaccines — from flu shots to shingles vaccines — contain an adjuvant, and the Centers for Disease Control and Prevention (CDC) says these substances have been used widely and safely for decades, in some cases for nearly 100 years. However, members of a federal vaccine panel recently appointed by Health and Human Services Secretary Robert F. Kennedy Jr. are scheduled to discuss adjuvants at a Dec. 5 meeting, raising concerns among some doctors and public health experts that the group may try to remove adjuvants from vaccines or raise doubts about their safety.

A focus on aluminum

Aluminum, the most common vaccine adjuvant, has been at the center of misinformation in recent years, including claims linking it to autism and other health issues.

The American Academy of Pediatrics, however, says that studies have found no significant health risks associated with the tiny amounts of aluminum salts in vaccines.

An observational study published in 2022 identified a possible association between exposure to aluminum from vaccines and asthma. “However, multiple larger studies have not shown such an association,” Dr. Jesse Goodman, an infectious disease physician and professor of medicine at Georgetown University, explained during a Dec. 2 briefing. What's more, a large Danish study published this year in the Annals of Internal Medicine found no evidence of an increased risk for autoimmune, allergy or neurodevelopmental disorders associated with the adjuvant.

“It’s been used around the world in any number of vaccines since 1926. Billions of people have received vaccines with aluminum, and the FDA here and the FDA equivalents around the world and in other countries, the World Health Organization, have all looked at this very carefully and found it to be not a safety issue at all,” Schaffner says.

Aluminum may sound like an unusual ingredient for a vaccine, but it’s a common metal found in the Earth’s crust, and it’s present in our everyday diets, Goodman explains.

Adjuvanted vaccines typically contain a half milligram or less of aluminum per dose, Goodman says, while our daily aluminum intake from food and water ranges from 7 to 9 milligrams.