Rabies vaccine is good in adult (over 1 year old) dogs and cats for 3 years, if they have prior vaccination. Vaccine is good for only 1 year if animal is 3 months to 1 year old, or 1 year for all dogs and cats with no prior vaccination. Vaccine is good for only 1 year for ferrets. Ferrets must be vaccinated annually.
Animals must be 3 months old before a rabies vaccine can be given. Maryland law requires that each person who owns or keeps a dog, cat, or ferret that is 4 months or older shall have the dog, cat, or ferret vaccinated adequately against rabies.