Which vaccination is NOT part of a combined antigen vaccine?

A combined antigen vaccine contains multiple antigens that protect against several diseases in a single shot, which enhances patient compliance and reduces the number of injections required. The correct answer, rotavirus, is not part of any currently available combined antigen vaccine in routine immunization schedules; it's typically administered as a standalone vaccine.

In contrast, diphtheria and tetanus are components of the diphtheria-tetanus-pertussis (DTaP) vaccine, which is designed to immunize against all three diseases simultaneously. Hepatitis B is also often included in combination vaccines, such as the pentavalent vaccine, which covers five different diseases, including Hepatitis B. Therefore, the rationale behind identifying rotavirus as the correct response lies in its unique position as a single-antigen vaccine, separate from the combination formulas that include diphtheria, tetanus, and hepatitis B.