Which of the following vaccines contains a synthetic adjuvant?

Heplisav is the vaccine that contains a synthetic adjuvant, specifically a novel adjuvant known as CpG 1018. This adjuvant is designed to enhance the immune response to the vaccine, which helps to provide stronger and longer-lasting protection against hepatitis B. Utilizing a synthetic adjuvant represents a newer approach in vaccine formulation, aiming to improve the efficacy of the vaccine with fewer doses.

In contrast, Havrix, Engerix, and Recombivax do not utilize synthetic adjuvants; instead, they typically rely on the traditional aluminum hydroxide as an adjuvant to stimulate the immune response. This difference in adjuvant technology highlights the innovation in Heplisav's development, contributing to its unique properties compared to other hepatitis B vaccines.