Dr. Lila Miller, ASPCA
One of the biggest controversies in companion animal medicine today surrounds the use of vaccinations in companion animals. Vaccines were developed initially to protect animals against deadly contagious diseases. Many diseases that were fairly common such as canine distemper, canine parvo, and feline panleukopenia are seen much less frequently today as a result of the intense efforts by the veterinary profession to vaccinate against them. In the case of rabies, the effort to routinely vaccinate dogs that began in the 1950s also dramatically reduced the incidence of cases of human rabies in this country. In some cases, vaccinations have been wildly successful in decreasing, if not practically eliminating the incidence of some diseases.
In small animal medicine, vaccines have traditionally been developed against diseases caused by viruses, bacteria and fungi. In newer developments, vaccines have been developed against protozoans like Giardia as well. Now it seems that vaccines are developed almost routinely in response to diseases regardless of how common they are or whether or not they have a fatal outcome. In fact, vaccine use is so widespread that most veterinary practices send reminder cards to clients to schedule appointments for their pets based solely on their vaccination schedule. Although it was well known that vaccines do cause reactions or have side effects, until recently it was thought that they were fairly rare, minor and treatable when they occurred, and far outweighed by their benefits. It is now believed that reactions may be more common and serious, and because of this concern, the debate has heated up about the judicious and appropriate use of vaccination.
How do vaccines work?
Vaccination, or active immunization, refers to the production of an active immune response in the body. Vaccination works by stimulating the immune system with either a weakened (modified-live or attenuated) or killed form of the disease organism itself. Vaccines are thus classified as modified-live or killed. The weakened or killed disease organism is referred to as an antigen. The body’s reaction to the introduction of the foreign antigen in the form of a vaccine injection is to mount a humoral (antibodies or immunoglobulins) or cell-mediated response. This is the defense system the body normally uses against disease. When the body encounters the real disease later on, it is already prepared to defend itself because of the prior exposure to the vaccine strain of disease. (It is important that the vaccine strain of disease closely match the actual disease strain.) If vaccination was successful in preparing the immune system, the range of response to infection can range from no clinical symptoms at all to mild disease.
Immune responses that are stimulated by modified-live vaccines occur faster and last longer than those from killed vaccines. The drawback is that modified-live vaccines have been known to cause disease in weakened, immune-compromised or otherwise debilitated animals. Killed vaccines are technically safer because they can’t cause disease, but the response takes longer and doesn’t last as long. Killed vaccines also require the use of adjuvants which are irritants designed to prolong and enhance the immune response. These adjuvants are under investigation for a possible association with serious vaccine reactions.
Vaccination works best in a healthy, unstressed animal. It takes about 7 days for the body to produce its response. Although most vaccines are given by injection, there are intranasal vaccines that are given as eye and nose drops. Because these vaccines are following the natural route of infection of respiratory diseases, the immune response may be produced much faster, within 72 hours, and last longer.
It is important to understand that vaccines do not make sick animals well, cure disease or prevent animals from becoming infected with the disease organism. They prevent serious illness only if the vaccine is given far enough ahead of the disease exposure for the animal’s own immune system to produce a quick defense before too much damage is done. Concurrent vaccination with or after disease exposure, a problem commonly encountered in shelters, is likely to result in vaccination failure.
The current vaccination controversy
There are several questions being asked about the costs/risks/benefits of vaccinating companion animals and the safety of the vaccines. Should animals be vaccinated against diseases that respond readily to therapy or that are not very common if it places the animal at risk for serious side effects? The questions most commonly asked relate specifically to:
- The number of vaccines in use
The number of vaccines available to veterinarians has skyrocketed in the last thirty years. The antigens have been combined into multivalent vaccines that allow one convenient injection to be given against several diseases, such as the common 5 in 1 DHLPP (distemper, hepatitis, leptospirosis, parainfluenza, parvo) dog vaccine. Questions have been raised about the effectiveness of these vaccines as well as the need for all the various components. Some other canine vaccines include Corona, Lyme, Heartworm, Bordetella, Ringworm, and Giardia.
- The need to vaccinate against mild diseases that respond readily to treatment
The use of some of the vaccines has been questioned when diseases such as corona are not only low in incidence, but also fairly mild, usually require no treatment or are easy to treat when they do occur.
- The fact that some vaccines are limited in their effectiveness.
Some vaccines are limited in their effectiveness, such as the Feline Infectious Peritonitis (FIP) vaccine for cats, and not recommended for general use.
- Vaccinations may interfere with later disease testing
Lyme Disease is difficult to diagnose in animals that have been vaccinated against the disease. It is also generally not as serious in dogs as it is in people. It responds readily to antibiotics in the early stages of the disease, yet treatment may be delayed because of the problems associated with diagnosis in vaccinated animals. Some veterinarians have questioned the need for a Lyme vaccine at all.
- The need for annual boosters.
In human medicine many vaccines confer long term, if not lifelong immunity. The search for explanations about the need for annual boosters in animals led many to the conclusion that the manufacturer’s recommendations may have been arbitrary and not based on duration of immunity studies at all. No one seemed to know exactly how long an animal would still be considered protected after vaccination. The studies now being conducted to find out how long an immune response can last in a vaccinated animal have revealed that many of the common vaccines confer “immunity” for several years if properly administered. In some cases, the titer may be taken instead of giving a booster. A titer is a blood test that will reveal the level of antibodies found in the blood. This functions as a measure of the immune response, although some would argue that the only true test of immunity is to “challenge” the animal with the disease and see if the animal becomes ill.
- The safety of the vaccines .
The debate about the safety of vaccines became very heated when a possible link between cat vaccinations and a certain form of a deadly cancer known as fibrosarcoma was discovered. It was also suspected that autoimmune hemolytic anemia in some dogs might have one of its links to vaccinations. Intensified research into the production of safer vaccines began largely as a result of the concerns about these two serious problems. In the meantime, veterinary immunologists, epidemiologists, internists and research specialists are examining the way vaccinations are given and proposing new protocols.
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