Minor quibble, vaccine protect against more than just viruses. Tetanus, for example, is a bacterial infection and there is a vaccine.

I think your general point stands that preventative medicines of all kinds have high value. From a technical standpoint, they are different types of medication.

Vaccines teach immune systems how to recognize and attack diseases and pathogens. These sorts of medications and treatments directly poison the parasites. They’re similar in effect in that the pets are defended against unwanted aggressors, but differ in the mechanism.