What is a vaccine adjuvant?

Adjuvants are added to some vaccines to make the immune system notice the vaccine more effectively. They can improve protection, reduce the amount of antigen needed, or help produce a stronger and longer-lasting response. One widely used adjuvant is aluminum salt, which has been used in vaccines for many decades. Not every vaccine contains an adjuvant; for example, many mRNA vaccines rely on the immune activity of the platform itself rather than a traditional adjuvant. Adjuvants have been carefully studied for safety and are a standard part of modern immunization science.