A vaccination refresher course


My daughter recently needed a “sports physical” for school. “She’s due for a diphtheria shot,” my husband reported upon their return, “but we postponed it. She doesn’t want a sore arm when she rides in the horse show tomorrow.” I sighed. My daughter’s world revolves around horses.

He continued with a complicated tale about insurance, doctor visits, and when she should go back for the vaccine. As he rambled on, I thought “Diphtheria? Really? Does anyone get diphtheria any more?” I thought about Balto, the famous Siberian husky who hauled diphtheria antitoxin across Alaska during the 1925 outbreak. I thought that I know less about my kids’ vaccinations than I know about my dog’s.

I thought pet owners could probably use a vaccination refresher course. So the first thing I want to say is vaccines are good. We are privileged to live in a time and place where few people die from measles, polio, tetanus, rabies. Not everyone is so lucky. Sure, it also makes sense to evaluate what vaccines are truly needed and balance benefits with risks, but that discussion is above my word limit. Today we’ll simply review the essentials. The purpose of vaccinations is to stimulate Balto’s immune system to make antibodies against specific diseases without actually causing illness. Then, if he ever encounters the real virus in nature, his body quickly “remembers,” pumping out antibodies to block infection. Vaccines for viruses such as rabies and distemper are either “killed,” “modified live,” or “recombinant.”

Killed vaccines contain relatively large doses of dead virus. This cannot cause infection, but when injected into Balto’s body, promotes formation of antibodies that are also effective against real, virulent disease. Modified live virus (MLV) vaccines use live organisms that are altered to not produce illness. MLV vaccines provoke stronger antibody responses with much smaller amounts of virus and usually result in better immunity. Recombinant vaccines utilize genetic engineering to further refine specific immunizations. Let’s take eight-week-old Baby Balto. Why does he need to keep coming back and forth for all those puppy shots? In the first days of life, Balto nurses, imbibing a special milk called colostrum which contains “passive maternal antibodies.” These give him some degree of temporary protection against disease but also interfere with his own immune response to vaccination. The series of vaccines are designed to protect Balto through that vulnerable time when passive maternal antibodies are waning and his own immune system is maturing. Even adult animals who are being vaccinated for the first time benefit by following initial vaccines with “booster” shots. The immune response to the second dose is faster and stronger and really “boosts” protection. “Only give him the shots he really needs, Doc,” some clients say. Well, that requires clarification. The only vaccine legally required for dogs and cats is rabies. You can decline all other vaccinations…but I wouldn’t recommend it. Veterinarians now classify immunizations into “core” and “non-core” categories.

Core vaccines for dogs are canine distemper, parvo, and rabies. Virtually every dog should receive these. Distemper used to kill huge numbers of dogs. Although far less common now, it is an extremely deadly disease. Parvo? Highly contagious. Often fatal. When the disease first appeared in the 70s, I worked in the “parvo wards” at the University of Pennsylvania veterinary hospital. There was no parvo vaccine back then. I watched dozens upon dozens of puppies die terrible deaths. I cannot imagine why anyone would refuse to protect their dog with an inexpensive, safe injection. Rabies? Think Ol’ Yeller. It’s a no-brainer. Rabies kills animals. It kills people. Horribly. So if you ask me what Balto really needs, I’ll tell you he needs core vaccines. “Non-core” vaccines include Lyme, leptospirosis, kennel cough, canine influenza, and several others. The decision whether to use these depends on your particular situation, Balto’s risk of exposure, and general health. Although not an official core vaccine, after 30 tick-filled years of Vineyard living, I strongly recommend Lyme vaccination in all dogs.

Kennel cough, on the other hand, is often a mild, self-limiting disease. I suggest it primarily for dogs with high exposure risk, i.e., those that frequent boarding kennels, groomers, and dog parks. Frequency of vaccination is another common concern. Legally, veterinarians may be held liable if they do not advise re-vaccination based on manufacturer’s recommendations. Since testing for “duration of immunity” is expensive, we often don’t really know how long protection lasts from each vaccine. We have therefore taken a “better safe than sorry” approach. However, with growing concern about possible risks of over-vaccination, combined with more data on long term immunity, guidelines for some vaccines such as distemper now suggest every three years to be adequate in most circumstances.

Another alternative to frequent distemper-parvo shots is a “vaccine titer,” checking antibody levels in Balto’s blood. Although not a guarantee, high antibody levels suggest persistent immunity. Some veterinarians will forego distemper-parvo boosters if Balto’s titers are good. Vaccines against bacterial diseases are usually less effective than those for viruses and duration of immunity is often significantly shorter. Thus, for bacterial diseases like Lyme, annual boosters are truly warranted. Frequency for rabies vaccination is determined by state law. I looked up diphtheria on the CDC website. The last reported case in the U.S. was in 2003 — an elderly traveler who contracted the disease in Haiti — but outbreaks causing significant illness and death commonly occur in developing countries, where fewer people are vaccinated. The section on clinical presentation described a firm, fleshy, grey, adherent pseudomembrane affecting tonsils, throat, nasal passages, and trachea. It bleeds easily if one attempts to remove or dislodge it and can actually cause fatal airway obstruction. Sounds awful.

I think of those parents in Alaska in 1925, waiting and wondering if the medicine would arrive by dog sled in time to save their children. And I think “How lucky are we? That we can protect our loved ones, both human and canine, with a quick trip to the doctor, or the vet, for a vaccination.”