Which of the following is administered by intramuscular (IM) injection?

Intramuscular (IM) injection is a method used to administer certain vaccines where the vaccine is injected deep into the muscle tissue, allowing for faster absorption into the bloodstream. Tdap, which is the vaccine for tetanus, diphtheria, and pertussis, is specifically recommended to be given via IM injection.

This is due to the formulation and the need for effective immunogenicity that the IM route provides for the components of the Tdap vaccine. By administering it intramuscularly, the body can best respond to the antigens present in the vaccine, producing the necessary immune response effectively.

On the other hand, the Varicella (VAR) vaccine, which protects against chickenpox, is typically administered as a subcutaneous injection, meaning it is injected into the fatty tissue just beneath the skin rather than the muscle. This route is most suitable for live attenuated vaccines like Varicella.

The choice highlighting both Tdap and Varicella or Varicella and MCV4 suggests that other vaccines, including Varicella, are inaccurately aligned with the IM injection route, when in fact, they are not. Thus, Tdap stands out as clearly requiring IM administration.