VACCINE RECOMMENDATIONS

• 1. Which vaccines should all cats receive?
  The core vaccines that all cats should receive include:

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    Panleukopenia (feline parvovirus)
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    Rhinotracheitis (feline herpesvirus 1)
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    Calicivirus
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    Rabies
• 2. Should other vaccines be considered?
  Noncore vaccines that should be administered on the basis of medical risk include:

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    Feline leukemia virus (FeLV)
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    Feline infectious peritonitis (FIP)
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    Chlamydia psittaci
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    Bordetella bronchiseptica
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    Giardia spp.
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    Microsporum canis
• 3. What types of vaccines are currently available?

  Attenuated (modified-live) vaccines generally have low antigen mass and almost never induce local reactions; they can be given locally (e.g., modified-live B. bronchiseptica intranasal vaccine) or parenterally (e.g., modified-live panleukopenia). However, living vaccines must replicate in the host to stimulate an effective immune response.

  Noninfectious vaccines include killed virus, killed bacteria (bacterins), and subunit vaccines. In general, noninfectious vaccines require higher antigen mass than modified-live vaccines to stimulate immune responses because they do not replicate in the host. Noninfectious vaccines stimulate immune responses of lesser magnitude and shorter duration than attenuated vaccines, unless adjuvants are added. Adjuvants improve immune responses by stimulating uptake of antigens by macrophages, which present the antigens to lymphocytes. Adjuvants can cause or potentiate adverse vaccine reactions; induction of vaccine-associated sarcomas in cats may be one example (see Chapter 82). Most adjuvanted vaccines studied in cats have led to pyogranulomatous reactions that may undergo malignant transformation to soft tissue sarcomas. Subunit vaccines may be superior to killed vaccines that use the entire organism because only the immunogenic parts of the organism are used; thus the potential for vaccine reactions is decreased.

  Vector vaccines combine the advantages of attenuated and subunit vaccines. The DNA that codes for the immunogenic components of the infectious agent is inserted into the genome of a nonpathogenic organism (vector) that replicates in the vaccinated species. As the vector repli cates in the host, it expresses the immunogenic components of the infectious agent, resulting in induction of specific immune responses. Because the vector vaccine is live and replicates in the host, adjuvants and high-antigen mass are not required, and because only DNA from the infectious agent is incorporated into the vaccine, there is no risk of reverting to the virulent parent strain, as occasionally occurs with attenuated vaccines. Only vectors that do not induce disease in the vaccinate are used.

• 4. Does the duration of immunity conferred by a vaccine vary?

  In general, modified live virus vaccines and vector vaccines provide better cell-mediated immunity and longer duration of humoral immunity than killed or inactivated vaccines.

• 5. Should all adjuvanted vaccines be avoided in cats?

  Because of the risk for vaccine-associated sarcomas (see Chapter 82), the nonadjuvanted product should be used when both adjuvanted and nonadjuvanted products are available. Many killed vaccines contain adjuvants, a fact that may not always be indicated on the label. Some killed feline rhinotracheitis, calcivirus, and panleukopenia (FVRCP) vaccines contain adjuvants and should not be used routinely. In addition, Microsporum canis and Giardia spp. vaccines contain adjuvants and should be avoided unless medically necessary.

• 6. Does the level of protection vary among vaccines for various diseases?

  Some vaccines provide sterilizing immunity; infection is totally prevented if the animal is exposed (e.g., panleukopenia). Other vaccines, including those for upper respiratory disease, do not prevent infection but limit clinical signs if vaccinated cats are exposed. In general, vaccination should be expected to provide no better immunity than that conferred by recovery from the disease.

• 7.
  How often should core vaccines be given to pet cats?

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    Kittens presented for vaccination between 6 and 12 weeks of age should be given an inactivated or modified live FVRCP vaccine every 3–4 weeks until 12 weeks of age.
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    Kittens presented at > 12 weeks of age should be given either 2 inactivated FVRCP, 3–4 weeks apart, or 1 modified live FVRCP.
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    Rabies vaccination should be based on local ordinances.
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    Core vaccines should be boosted in 1 year, then every 3 years thereafter unless a rabies vaccine approved only for 1 year is used (see question 9).
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    Titer and challenge studies indicate that core vaccines are effective for more than 6 years; for some antigens, such as panleukopenia, duration of immunity is probably lifelong.
• 8.
  How should the core vaccines be administered?

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    Topical (intranasal) and injectable FVRCP vaccines are available.

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      Intranasal rhinotracheitis and calicivirus vaccines induce IgA antibodies more rapidly and should be used if speed of response is important (e.g., during outbreaks).
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      Intranasal vaccines often are associated with sneezing.
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      Intranasal vaccines are not as likely as injectable vaccines to cause vaccine-associated sarcomas.
  • 2.
    Injectable FVRCP vaccines should be administered subcutaneously as low as possible over the right shoulder.
  • 3.
    Rabies vaccines should be given intramuscularly or subcutaneously as low as possible on the right rear limb.
• 9. Which rabies vaccines should be used in cats?

  One nonadjuvanted rabies vaccine (Merial, Athens, GA) is currently available; at this time, it is the rabies vaccine of choice for cats. Chronic inflammation is thought to be necessary for the development of vaccine sarcomas (see Chapter 82); this product induces no chronic reaction at the injection site.

• 10. How often should core vaccines be given in crowded environments such as catteries or shelters?

  If outbreaks occur, modified live intranasal vaccines containing feline herpesvirus 1 and calicivirus have been given to kittens as young as 2 weeks of age. In this scenario, one vaccine is usually divided among several kittens.

• 11. Why not use an interval longer than 3 years?

  Memory T-lymphocytes probably exist for a lifetime after the administration of a modified live virus vaccine; thus vaccination intervals for some antigens probably could be longer. If recovery from the natural disease results in lifelong immunity, prolonged immunity may be expected from vaccination. Evolutionary concepts suggest that cats that are susceptible to acutely fatal diseases twice would be purged from the gene pool. For example, panleukopenia has never been reported in a cat that has received the initial set of vaccines, regardless of whether they received additional booster vaccines.

• 12. Can serum antibody titers be used to determine need for boosting individual cats?
  Serum antibody titers are an indirect measure of protection that may be used for some diseases, but they have limitations:

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    Reproducibility from laboratory to laboratory is sometimes poor; only laboratories that have correlated titer magnitude to protection should be used (New York State Diagnostic Laboratory, Ithaca, NY; HESKA Diagnostic Laboratory, Fort Collins, CO).
  • 2.
    For some diseases, mucosal and cell-mediated immunity is more important than humoral immunity for protection.
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    The presence of antibodies against panleukopenia, herpesvirus 1, and calicivirus usually predicts protection, but the absence of antibodies does not accurately predict susceptibility.
• 13. When should FeLV vaccination be used?
  Cats that benefit the most from FeLV vaccines are young cats with a high risk of contact with FeLV carriers. For example, when exposed to an FeLV-infected cat, 12-week-old kittens and adult cats have an 85% and 15% chance, respectively, of becoming persistently infected. This age-acquired immunity limits the protection that can be attributed to the FeLV vaccine in adult cats.

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    Naive cats should receive 2 vaccinations initially.
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    Adjuvanted products should be administered subcutaneously or intramuscularly in the distal left rear limb because of the risk for development of soft tissue sarcomas.
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    Because duration of immunity is unknown, annual boosters are currently recommended.
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    The vaccine is not effective in persistently viremic cats and so is not indicated. However, administration of the vaccine to viremic or latent cats is not associated with an increased risk of vaccine reaction.
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    FeLV testing should be performed before vaccination because the retrovirus serologic status of all cats should be known to maintain appropriate husbandry.
• 14. When should FIP vaccine be used?

  The incidence of FIP is only 1 in 5000 cat households. The vaccine has been shown to be effective only in cats that do not harbor the coronavirus. Given that 20–40% of cats already harbor the coronavirus, that the maximal protection of the vaccines is 60–80%, and that the duration of protection is limited to secretory IgA, the value of the FIP vaccine in any situation is questionable. The vaccine may be indicated for seronegative cats entering a household or cattery known to be FIP-infected.

• 15. Should cats be vaccinated against chlamydiosis?

  In the United States, Chlamydia psittaci infection in cats generally results only in mild conjunctivitis; therefore, whether vaccination is ever required is controversial. Use of this vaccine should be reserved for cats with a high risk of exposure to other cats and in catteries with endemic disease. Duration of immunity for chlamydial vaccines may be short-lived; thus, high-risk cats should be immunized before a potential exposure.

• 16. Should cats be vaccinated against bordetellosis?

  Many cats have antibodies against B. bronchiseptica, and there are sporadic reports of severe lower respiratory disease due to bordetellosis in young kittens from crowded, stressful environments. Clinical infection in pet cats, however, is extremely rare. B. bronchiseptica vaccination should be considered primarily for cats at high risk for exposure. Because the disease is apparently not life-threatening in adult cats, is uncommon in pet cats, and responds to various antibiotics, routine use of the vaccine in client-owned cats seems unnecessary.

• 17. Should cats be vaccinated against giardiasis?

  A Giardia spp. vaccine has been introduced for use in cats. When given twice, the vaccine lessens numbers of cysts shed and clinical disease on challenge with one heterologous strain. The vaccine is adjuvanted and given subcutaneously and ultimately may be associated with fibrosarcomas. Because the disease is usually not life-threatening and at least 90% of cases respond to therapy, routine use in client-owned cats seems unnecessary. The vaccine may have therapeutic utility in cats with recurrent or persistent infection, as was recently documented in dogs.