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Veterinarian Technician October 2006 (Vol 27, No 10) Focus: Exotics

Vaccination Overview

by Ann Wortinger, BIS, LVT, VTS (ECC, SAIM, Nutrition)

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    Key Points

    • Vaccinating dogs and cats against disease is an important part of preventive medicine.
    • Individual animals may require different vaccine protocols based on various factors, including probability of exposure, previous vaccination history, and lifestyle.
    • As with any medical procedure, the staff should explain to the client both the benefits and risks associated with vaccinations.

    Although animal vaccines play an important role in protecting companion animals as well as the humans who care for them, the balance between the risks and benefits of vaccination is continually being reassessed. Evolving guidelines, ongoing research, and increasing client awareness make it important for every member of the veterinary staff to keep informed of the latest developments so that they can give their patients the best care possible.

    Principles of Vaccination

    The main objective of vaccination is to limit or protect against infection and disease. The frequency and type of vaccine to be administered depends on many factors, including the lifestyle of the pet being vaccinated (e.g., indoor vs. outdoor), travel and kennel/boarding plans, underlying disease (e.g., immune-mediated diseases), preexisting conditions,1 risk of exposure, potential severity of the disease, efficacy and safety of the vaccine, public health concerns, and owner preference.2 Because these factors may change, the patient's vaccination protocol should be reassessed during routine annual examinations.1 A clinic's overall vaccination protocol should aim to immunize as many animals as possible in the at-risk population, to vaccinate each animal only as often as necessary to provide adequate protection, to vaccinate against only the infectious agents to which each animal may realistically be exposed and subsequently develop disease, and to minimize the potential for adverse events.2,3

    Meeting these goals requires that each patient be assessed individually for disease risk. In 2001, the AVMA's Council on Biologic and Therapeutic Agents (COBTA) stated that variation in patients, patient lifestyles, and the available vaccine products "requires a customized approach to vaccination recommendations to best match the variation in the patients presented for immunization."2 This thinking is reflected in the 2006 American Animal Hospital Association (AAHA) Canine Vaccine Guidelines, which also agree with COBTA in making it clear that vaccination decisions should be undertaken in the context of discussion with the owner. Therefore, for owned pets, an established doctor-client"patient relationship should be used to determine which vaccines are necessary for each animal.2,4

    Types of Vaccines

    In general, vaccines introduce an antigen into the body to stimulate the production of antibodies by the immune system. Most vaccines used in dogs and cats fall into one of the following categories: modified live, killed, recombinant subunit, or recombinant vector.5

    Modified Live

    Modified live vaccines contain a weakened, or attenuated, form of the pathogen of interest. Organisms are weakened in the laboratory through manipulation of their growing conditions. When the vaccine is administered to the animal, the pathogen replicates but does not usually cause clinical disease. However, if the pathogen is not attenuated enough or if the animal receiving the vaccine is immunosuppressed, a mild form of the disease may result.6 Modified live vaccines rarely cause hypersensitivity and usually do not require revaccination.7 In addition, they generally provide a longer duration of immunity than killed vaccines for the same virus.7

    Killed

    Killed vaccines, like modified live vaccines, introduce the entire pathogen of interest into the body. Because the pathogen is dead, however, these vaccines cannot cause disease.8 Killed vaccines require an adjuvant as well as more frequent boosters in order to sufficiently stimulate the immune system, which may increase the chance of a local reaction.6 Killed vaccines also have a shorter duration of immunity than modified live vaccines.8

    Recombinant Subunit

    To avoid the need to introduce the whole pathogen, some vaccines have been designed to contain only particular, non-disease-causing proteins that are normally produced by the pathogen. To generate large enough quantities of the protein, the gene for the protein is removed from the pathogen and inserted into a different organism. The new, genetically altered organisms are grown in the laboratory and the protein harvested and concentrated into the vaccine. Antibodies that are created by the immune system to recognize these proteins will then recognize them if they encounter them as part of an invading pathogen.5 An advantage of recombinant subunit vaccines is that they require reduced levels of antigen for immune stimulation.4 However, more than one protein may be needed to provide protection against disease and the proteins are very specific.4

    Recombinant Vector

    Isolating genes that encode for specific proteins from one organism and incorporating them into another can also be used to create non-disease-causing carrier, or vector, organisms. Rather than producing the proteins in the laboratory, the genetically altered organisms are administered directly to the animal in the vaccine. When the organism in the vaccine expresses the protein from the pathogen, the immune system creates antibodies to the pathogen's protein.5 An advantage of recombinant vector vaccines is that they can induce humoral and T-cell-mediated responses similar to those induced by modified live vaccines.4 In addition, there is no risk of reversion to virulence.4 These vaccines, however, may offer a lower level of immunostimulation compared with conventional live vaccines.9

    Current Vaccination Guidelines

    In early 2006, AAHA released its updated canine vaccine guidelines.4 These guidelines expand on the ones issued in 2003 and include information on new vaccine technologies, adverse event reporting, and medicolegal issues surrounding vaccination as well as a new section on vaccination in the shelter setting.

    The American Association of Feline Practitioners (AAFP) and Academy of Feline Medicine (AFM) Advisory Panel on Feline Vaccines is planning to release its updated feline vaccination guidelines in late 2006. The panel last released vaccination guidelines in 2000.3 Because individual animals have different vaccination needs, the COBTA report recommends that veterinarians create two vaccination protocols — core and noncore.2 Noncore vaccines are those that should be administered based on the veterinarian's assessment of the patient's individual risk for disease.2,4

    Core Vaccines

    Core vaccines are those vaccines given to protect against the most prevalent, potentially life-threatening diseases or zoonotic diseases of substantial public health importance.2 The AAHA guidelines state that all dogs should receive core vaccines in one form or another.4 Any vaccine that is required by law, such as rabies, is considered a core vaccine.2

    Noncore Vaccines

    The decision to administer a noncore vaccine is based on the veterinarian's knowledge of a particular animal's risk of exposure and includes consideration of variables such as age, geographic location, and lifestyle.4 Risk assessment sheets can be devised to allow the veterinarian to determine which noncore vaccines or tests the patient may need. Practices may consider including noncore vaccines in their own core vaccination policy if particular diseases are known to be endemic to the area, or they may wish to create a separate noncore vaccination policy.2,4

    Vaccination Schedules

    In recent years, vaccination recommendations have become highly controversial in veterinary medicine. Not every expert agrees as to which vaccines should be given and how often, unless specified by law. According to COBTA, "kittens and puppies under 16 weeks of age represent the most susceptible age group."2 This group is "the principal target population for vaccination" because they experience "the highest rates and most severe cases of disease."2 Some guidelines recommend that puppies and kittens get their initial series of core vaccines starting at 6 weeks of age, with revaccination done every 3 to 4 weeks until at least 12 weeks of age.3,4 Some vaccine manufacturers, however, recommend that their product be given when the animal is slightly older.1 Therefore, it is important for veterinarians to be familiar with the current research as well as the manufacturer recommendations when administering vaccines.

    The practice of revaccinating animals annually is also being debated. According to the COBTA, "there is increasing evidence that some vaccines provide immunity beyond 1 year."2 Because the animal's lifestyle and risk are subject to change, the pet should be examined at least once yearly and its vaccination protocol should be reassessed at that time.

    Some practice owners have suggested that core and noncore vaccinations can be staggered so that no more than one to two vaccinations are given at any one visit, with wellness exams occurring every 6 months instead of yearly. This schedule allows the veterinary team the opportunity to examine the pet on a more regular basis.

    In cats, intramuscular administration of vaccines does not lessen the risk of tumor formation but may delay detection by the owner and may result in more advanced disease and a poorer prognosis if a tumor is eventually detected.10 (For more information about injection site sarcomas, see "Injection-Site Sarcomas in Cats," which starts on page 140 of the February 2005 issue.)

    Duration of Immunity

    The current duration of immunity listed on vaccine labels is the minimum duration of immunity, based on efficacy studies conducted by vaccine manufacturers.4 However, there is evidence that some vaccines provide immunity for a longer period than the label claims.2,4 The 1-year revaccination recommendation found on many vaccine labels is based on historical precedent and USDA regulation, not on scientific data.2 Actual duration of immunity for any vaccine is influenced by such factors as the vaccine manufacturing process, route of administration, concentration of antigen in the product, product handling, health status of the animal at the time of vaccination, and genetic variances in an individual animal's ability to respond to a vaccine.11

    Controversial Issues

    Adverse Reactions to Vaccination

    Vaccination provides significant benefits, but it is not without risk. Adverse events may be associated with any part or combination of parts of a vaccine: antigen, adjuvant, carrier, or preservative.12 Possible adverse reactions to vaccines include anaphylaxis, immunosuppression, autoimmune disorders, and transient infections.12 Because injection-site sarcomas are a possible risk in cats,8 vaccines should be given according to the vaccination sites recommended by the AAFP/AFM Advisory Panel on Feline Vaccines.3 Occasionally, an immunocompromised animal, or even a healthy animal under unfavorable environmental and genetic conditions, may fail to mount an immune response to a vaccine, resulting in lack of protection.6 However, for the core vaccines, benefits generally outweigh risks.

    The clinical syndromes associated with nonanaphylactic vaccine reactions are generally vague and can mimic a variety of other diseases. They include fever, malaise, stiffness, immunosuppression, autoimmune responses, and neurologic complications.5 Certain breeds of dogs (e.g., Akita, weimaraner) may be more prone to certain adverse events.6 However, it is difficult to estimate the actual rate of adverse events because reactions are more likely to be reported to the individual manufacturer; no one central reporting agency exists to gather this information.

    In patients with severe adverse vaccine reactions, practitioners may decide to withhold future vaccination. In these cases, antibody titers may be measured instead. In general, the AVMA's COBTA report states, "Unnecessary stimulation of the immune system does not result in enhanced disease resistance and may expose animals to unnecessary risks."2

    Titers

    The role of antibody titers in determining adequate protection against viral infection is still under debate. Vaccines are thought to elicit both a humoral (antibody-mediated) and a cell-mediated immune response. A humoral response can be readily measured by the detection of pathogen-specific antibodies (titers). In contrast, measurement of cell-mediated immune response is difficult and is not typically performed on a routine basis.13 For many infectious agents, it is unknown whether the relevant protective immune response is antibody- or cell-mediated, and it is likely that both areas of the immune system are involved to varying degrees.13 Therefore, the absence of antibodies as identified through titers does not define susceptibility.11 That said, antibody titers probably correlate with immunity for some of the core vaccines,11 and the presence of antibodies to a disease-causing organism indicates that an animal has been exposed to that organism, either through infection or vaccination, and mounted an immune response. AAHA states that titers are "useful for monitoring immunity to canine distemper virus, canine parvovirus-2, canine adenovirus-1, and rabies virus and to ensure that an animal has responded to a specific vaccine."4

    Biologic agents, such as vaccines, are regulated by the USDA, not the FDA and, therefore, are not subject to the FDA regulations that pertain to extralabel use. As long as they are practicing in accordance with a given standard of care accepted by the profession, veterinarians have the legal authority to administer vaccines with discretion.14 Of course, rabies vaccination is the exception because it is required by law. The published guidelines do represent an accepted standard of care appropriate to the practice of companion animal medicine. Veterinarians who elect to follow the published guidelines in developing vaccination protocols are acting in accordance with a standard of care recognized by the veterinary profession.14

    The risks and benefits of vaccination should be discussed with the client before vaccines are administered. Clinics may choose to have their clients sign a form stating that they have been informed about the possibility of adverse events and that they consent to having their pet vaccinated. These informed consent documents may be of assistance in legal disputes; however, laws and standards of care vary by state. The AAHA and AAFP/AFM panel discuss the issue of informed consent in their respective guidelines, and the AAFP/AFM document includes sample consent forms.

    Vaccination in Context

    Although it is important to keep up with constantly evolving knowledge regarding vaccines and development of new technologies, it is equally important to emphasize the basics of good pet care to clients. During each visit, technicians can educate clients about the importance of having their pet vaccinated. They can also explain to clients the benefits of bringing their pets into the clinic for annual or even biannual physical examinations, laboratory testing, and dental prophylaxis. By fully explaining each part of the physical examination and the subsequent recommendations, technicians can ensure that clients are well informed about the "gold standard" of care needed by their individual pet. Early neutering and spaying of all companion animals, behavioral and nutrition counseling, year-round heartworm prevention in endemic areas, strategic deworming, and flea and tick prevention are other common subjects that technicians should address with clients.

    Conclusion

    As clients become aware of more and more choices for the care of their pets, it is the veterinary technician's re­sponsibility to give them the most current, scientifically reliable information. Technicians should be prepared to answer questions about their clinic's vaccination protocols as well as to address client concerns about the possibility of adverse events. By providing accurate, up-to-date information about vaccination, technicians can help clients make decisions about the best care for their pets.

    1. University of California-Davis: Canine and Feline Vaccination Guidelines. Accessed September 2006 at www.vmth.ucdavis.edu/vmth/clientinfo/info/genmed/vaccinproto.html.

    2. Klingborg DJ, Hustead DR, Curry-Galvin EA, et al: AVMA Council on Biologic and Therapeutic Agents' Report on Cat and Dog Vaccines. JAVMA 221(10):1401-1407, 2002.

    3. American Association of Feline Practitioners and Academy of Feline Medicine Advisory Panel on Feline Vaccines: 2000 Report of the American Association of Feline Practitioners and Academy of Feline Medicine Advisory Panel on Feline Vaccines. J Feline Med Surg 3(2):47-72, 2001.

    4. American Animal Hospital Association: 2006 AAHA Canine Vaccine Guidelines. Accessed September 2006 at http://www. aahanet.org/About_aaha/About_Guidelines_Canine06.html.

    5. Greene CE: Immunoprophylaxis and immunotherapy, in Infectious Diseases of the Dog and Cat, ed 2. Philadelphia, WB Saunders, 1998, pp 717-750.

    6. Tizard IR: Vaccination and vaccines, in Veterinary Immunology: An Introduction, ed 6. Philadelphia, WB Saunders, 2000, pp 235-252.

    7. Wolf AM: Vaccines of the Present and Future. Accessed Septem­ber 2006 at www.vin.com/VINDBPub/SearchPB/Proceedings/PR05000/PR00141.htm.

    8. Wolf AM: Vaccines, Viruses, Vaccinosarcoma — Truth or Fiction. Accessed September 2006 at www.vin.com/Members/Proceedings/Proceedings.plx?CID=acvc2002&PID=pr0250.

    9. Booth K: Recent Advances in Vaccinology — What Can We Expect from the Future? Accessed September 2006 at www.vin.com/Members/Proceedings/Proceedings.plx?CID=acvsc2003&PID=pr04899&O=VIN.

    10. Ford RB: Infection and immunization: The cat. Proc IVECCS Conf: 641-644, 2005.

    11. Ford RB: Infection and immunization: The dog. Proc IVECCS Conf: 635-639, 2005.

    12. American Veterinary Medical Association: Principles of Vacci­nation. Available at: http://www.avma.org/issues/policy/vaccination_principles.asp; accessed August 2006.

    13. Lappin MR: Use of serological tests to determine vaccine needs. Proc NAVC: 609-611, 2006.

    14. Ford RB: The Vaccination WebSite for Dogs & Cats: Hot Topics. Accessed September 2006 at www.dvmvac.com/HotTopic.html.

    References »

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