Visiting Vet: Vaccine reactions

Small breeds and dogs under the age of 3 years are at greater risk.

Labrador retriever — Augustus Binu

When Fiji, a Labrador retriever, arrived at my office at 8 weeks old, we began the usual puppy protocol. Examination, vaccinations, deworming, and so on. She arrived faithfully for each recommended visit. Why do puppies need so many appointments? Well, one reason is that young dogs are particularly susceptible to dangerous diseases like canine distemper and parvoviruses. If a mother dog is vaccinated before pregnancy, then maternal antibodies pass to her puppies, in utero and through nursing after birth, but these antibodies provide only temporary protection against disease. They can also interfere with the effectiveness of vaccinations. Maternal antibodies gradually disappear, leaving pups vulnerable again, usually sometime between 8 and 16 weeks of age, when a puppy’s immune system is not yet fully functional. In order to best protect Fiji, we give a series of “puppy shots” during this period when maternal antibodies are waning and her own immune system is maturing.

By the day of her third visit, Fiji had already received multiple vaccinations without missing a beat. Like many veterinarians, one vaccine I use is a combination product that includes canine distemper virus, parvovirus, adenovirus, and parainfluenza, all in one injection. We had given Fiji that combo previously, as well as rabies vaccination. These are “core” vaccines, recommended for all dogs to protect against deadly, highly infectious diseases, as well as those with public health significance. Fiji had also received several “noncore” vaccines, including Lyme and kennel cough. Noncore vaccines are administered based on individual risk determined by geography and lifestyle. A pampered Pomeranian in Manhattan may not need Lyme vaccination, but certainly should have kennel cough protection for those monthly visits to the grooming parlor. A Labrador on Martha’s Vineyard? Vaccinate for Lyme disease!

It was late afternoon when Fiji arrived for her final distemper-parvo vaccination. We weighed her, then I popped the shot, gave her a liver treat, and waved goodbye. I saw one last appointment, released a diabetic cat, reviewing instructions about insulin and feeding, said goodnight to staff, locked the door, and started cooking dinner. Just as we were sitting down to eat, the answering service sent a message. Fiji had been vomiting constantly ever since her vaccination two hours earlier.

Adverse vaccine reactions — the most common is a simple inflammatory response that can include pain, swelling at the injection site, and mild transient fever. This happens to people as well as pets. My daughter got a vaccine last month; her arm hurt for a week. If lethargy lasts more than a day or two, or if local inflammation persists longer than a week, call your veterinarian.

Fiji’s reaction was more serious — a true “allergic” reaction. This occurs when the immune system overreacts to any of a number of substances in the vaccine. Signs can include hives, rashes, swelling of head, face, and ears, vomiting, and diarrhea. The most serious reaction is full-blown anaphylaxis with difficulty breathing, shock, even sudden death. This extreme event is very rare in dogs. Vaccine reactions typically occur almost immediately post-vaccination, but things like hives may develop as long as one to two days later.

Other rare reactions to vaccination are theorized, though not proven, to be implicated in certain immune-mediated diseases such as immune-mediated hemolytic anemia or thrombocytopenia, or immune-mediated arthritis. None have been definitively proven, but many veterinarians advise caution when vaccinating individual dogs with a history of these diseases. (In cats, injections in general, and vaccinations in particular, have been linked to cancer, but that’s a whole other article.) Certain types of vaccines have been anecdotally reported as more likely to cause allergic reactions. Again, the scientific evidence is not definitive. The combo I gave Fiji that afternoon was not a vaccine linked to a high incidence of reactions, but any individual dog may have an allergic reaction to any individual substance.

Mild reactions are treated with antihistamines like diphenhydramine (Benadryl) and symptomatic care. More severe reactions require corticosteroids, or even epinephrine. Depending on the severity of the episode, future vaccination protocols should be modified appropriately. We don’t want to leave dogs unprotected from serious diseases, but we need to be cautious. In many cases, simply premedicating with antihistamines before vaccinating again is sufficient to prevent reactions. It is also prudent to give only one vaccine per visit, and to observe the dog closely afterward. In cases with very severe reactions, however, the risk of any future vaccination outweighs the possible benefits, and we just don’t take the chance.

How often do vaccine reactions occur in dogs? Not often. Studies suggest about one in every 250 dogs may have some sort of reaction, but this includes everything from sore legs to more serious issues. The incidence of truly life-threatening reactions is extremely low. Dogs under the age of 3 years are at greater risk, as are small breeds, especially dachshunds, pugs, Boston terriers, miniature pinschers, and Chihuahuas. Boxers also seem to have a higher incidence. Sometimes owners of small dogs ask veterinarians to give only half a dose of vaccine. This makes no sense scientifically. Let me put it this way. If your child is allergic to peanuts, is it safer if you just give half a peanut butter and jelly sandwich? No. The reaction is not dose-related. If your child is not allergic to peanuts, there is no reason not to give him a whole PB&J. Smaller doses do not change the risk of allergic reaction.

Fiji’s reaction was not life-threatening. We gave her an antihistamine injection and another medication to stop the vomiting, then sent her home with additional oral antihistamines to use if necessary. She responded immediately, and was soon back to her normal puppy self. We put alerts on her record and our computer, and told her parents to always remind me, or any veterinarian they see, that Fiji has had a significant vaccination reaction. If your pup has ever had a vaccine reaction, always speak up. Don’t wait until after the doc pops the shot!