Rabies is a highly contagious and fatal viral disease. In addition to dogs, it also affects cats and other mammals, including humans. Luckily, with proper vaccination, dog rabies is completely preventable. Keep reading to learn how the rabies vaccine works, the side effects of rabies vaccine in dogs and how to know if rabies vaccine side effects warrant going to the veterinarian.

How the Rabies Vaccine Works

All rabies vaccines administered in the U.S. and Canada are inactivated, or killed, meaning the virus has been processed so it can't cause disease. While most vaccines require two to four initial boosters, the rabies vaccine is a little different. Like other killed vaccines, the initial dose of a rabies vaccine triggers the immune system to be able to create antibodies that can fight rabies if the dog is ever exposed to the virus. Rabies is a slow-acting virus — it can take weeks to months to result in symptoms — which allows a dog's body time to mount an immune response and fight the infection. The rabies vaccine is so effective that it's very rare for dogs who've been vaccinated to become infected.

Vaccine antibodies wane over time, causing the rabies vaccine to lose its efficacy. This is why dogs must get follow-up booster doses. Dogs usually receive one booster a year after their initial shot and then get it once every one to three years to maintain immunity. In most areas, keeping your dog up to date on their rabies vaccine is required by law.

Common Side Effects of Rabies Vaccine in Dogs

Because vaccines work by stimulating the immune system, the side effects of rabies vaccine in dogs are usually due to a stimulated immune system. Side effects can include mild fever, mild loss of appetite and mild to moderate loss of energy for 24 to 36 hours after vaccination. It's also possible for dogs to experience soreness and mild swelling at the injection site. Some dogs don't experience any side effects at all. If side effects occur, they typically start within an hour of vaccination and subside within a day or two.

Occasionally, dogs develop a small, painless swelling at the injection site that can last for a couple of weeks. In rare cases, dogs may develop a small, circular area of hair loss at the site of injection.

Rare Side Effects of Rabies Vaccine in Dogs

Even though it's rare, a dog can have a severe reaction to the rabies vaccine. This typically isn't because there's something wrong with the vaccine itself, but is due to an overreaction of the dog's immune system.

Serious side effects usually start immediately after or within one hour of vaccination.

Rare reactions to the rabies vaccine include:

  • Hives, which appear as firm lumps all over the dog's body and may or may not be itchy
  • Vomiting
  • Diarrhea
  • Swollen face, muzzle and/or eyes
  • Severe pain or swelling at the injection site
  • Cough
  • Collapse or fainting

If you notice any of these signs, immediately take your dog to the veterinarian for emergency treatment.

What to Do If You Notice Rabies Vaccine Side Effects

Loss of energy for a day or two, mild fever, mild soreness and temporary loss of appetite all signal that the vaccine is doing what it's supposed to — stimulating the immune system. If you notice these signs, let your dog rest, shower them with tender, loving care and monitor them for a couple of days. If you're ever worried that your dog might be in pain, call your veterinarian and ask for advice. They may prescribe pain medicine to help your dog feel better.

If you're ever worried, don't hesitate to call your veterinarian. In general, however, it's not necessary to contact the veterinarian unless:

  • The mild, expected side effects worsen or continue longer than a few days
  • Your dog develops swelling at the injection site that's hot or painful, is weeping, gets larger or doesn't go away after a couple of weeks

Your dog develops any severe or abnormal reactions

Rabies Vaccine Alternatives

If your dog has an adverse reaction to the rabies vaccine, talk to your veterinarian. The laws in every state are different and your veterinarian will be your best resource on whether or not your dog can forgo the vaccine. As an alternative, a veterinarian can run a titer test, which evaluates the level of antibodies in the blood. This can help determine if there are enough antibodies present to defend against disease.

If your dog has had adverse reactions to vaccines in the past, discuss the risk of vaccination vs. the risk of infection with your veterinarian. If your dog is sensitive to the vaccine, your veterinarian may be able to control negative side effects by administering antihistamines or other medications before vaccination and monitor your dog for reactions post-vaccination.

Dr. Sarah Wooten Dr. Sarah Wooten

Dr. Sarah Wooten graduated from UC Davis School of Veterinary Medicine in 2002. A member of the American Society of Veterinary Journalists, Dr. Wooten divides her professional time between small animal practice in Greeley, Colorado, public speaking on associate issues, leadership, and client communication, and writing. She enjoys camping with her family, skiing, SCUBA, and participating in triathlons.