Viruses are unaffected by which of the following?

Viruses are unaffected by antibiotics because antibiotics are specifically designed to target bacterial infections. They work by interfering with the processes that bacteria need to grow and reproduce, such as cell wall synthesis or protein production. Since viruses operate differently from bacteria and do not possess the cellular structures or metabolic processes that antibiotics target, they are not susceptible to the action of these medications.

The other options involve treatments that can be used against viruses in various ways. Vaccines work by stimulating the immune system to recognize and fight off viruses before they can cause disease. Antivirals are medications specifically designed to treat viral infections by inhibiting viral replication. Antiparasitics, while primarily used against parasites, are not typically relevant to viral infections. Therefore, the choice reflecting the lack of effect on viruses is antibiotics.