The puppy vaccinations include parvo. Until the series is completed dogs are still susceptible. Unvaccinated dogs are susceptible. This virus is extremely contagious and lasts for a very long time in the environment (it can actually overwinter.) And, no vaccine is 100% effective. Booster vaccinations also contain parvo protection
We have achieved "herd immunity" with this disease in most areas so we don't see epidemics like we did in the 1980s, but this virus will probably never be eradicated and will be a potential pathogen for susceptible individuals.
We still see many cases and up to this point have had limited options as far as treatment.