Which of the following vaccines must be stored in a frozen state?

Zostavax, the shingles vaccine, must be stored in a frozen state to maintain its efficacy. This is crucial because the live attenuated virus in the vaccine can become ineffective if it is exposed to temperatures above the recommended freezing point. Proper storage conditions are necessary to preserve the viability of the vaccine, ensuring that patients receive the maximum benefit when vaccinated.

In contrast, the other vaccines listed have different storage requirements. Inactivated influenza and Tdap vaccines can be stored in the refrigerator and do not require freezing. Live attenuated influenza vaccine typically is also stored in the refrigerator, not frozen, as exposure to freezing temperatures can damage the virus, rendering the vaccine ineffective. Therefore, only Zostavax requires storage in a frozen state.