A few years ago, vaccination protocols for cats were well defined and accepted by the profession and the clients.  Because of the development of vaccine-induced fibro sarcomas, the benefit of vaccination has been questioned.  The effectiveness of cat vaccines has greatly diminished infectious diseases reducing the clients' familiarity with conditions such as panleukopenia, rabies and the viral respiratory diseases.  There is also a generalized distrust of science that is, in part, fostered by the popular press.  All this has required the reexamination of vaccination protocols for the cat.

 

The key factor in determining the best vaccination protocol is individualization of the vaccines given to fit the lifestyle of the cat. The following factors need to be considered in determining vaccine protocols: duration of immunity, severity of the disease, prevalence of disease in the area, efficacy of the vaccine and likelihood of adverse effects.

 

Duration of immunity depends on the antigen in the vaccine.  Panleukopenia virus produces an excellent duration of immunity.  Cats vaccinated against panleukopenia as kittens and revaccinated at a year of age are probably immune for life.  Scott et al showed significant reduction in duration and severity of clinical signs of herpesvirus and calicivirus infection up to

7.5 years after vaccination with a killed virus vaccine.  Cats challenged with virulent virus 3 weeks after vaccination for the respiratory viruses will develop clinical signs of respiratory disease.  The feline respiratory virus vaccines do not produce complete protection.  Fortunately, duration of immunity for rabies is well established through an aggressive challenge system.  The duration of immunity after feline leukemia virus vaccination depends on the vaccine used but is probably longer than 1 year.  Generally, bacterial vaccines such as Bordetella bronchiseptica vaccines produce immunity of short duration, probably less than 1 year.

 

The age of the cat when vaccinated influences the immune response.  Even in the absence of maternal antibodies, kittens under 3 weeks of age will not respond well to vaccination.  The vaccination for feline infectious peritonitis is not recommended until 16 weeks of age.  This creates difficulties because kittens in high risk environments are usually infected with enteric coronavirus by 16 weeks of age.  Intestinal infection with coronavirus precludes successful vaccination with the feline infectious peritonitis vaccine.  Poor nutritional status will also diminish response to a variety of vaccines.

 

Severity of disease affects the need for vaccination.  Rabies and feline infectious peritonitis are fatal while panleukopenia, herpesvirus and calicivirus infections can produce a great deal of morbidity.  Bordetella infections may occasionally kill cats.

Prevalence of infectious diseases in your cat population greatly influences the need to vaccinate. Panleukopenia is uncommon because of effective vaccination but it is likely to reemerge if vaccination against panleukopenia was discontinued.  The stability of the panleukopenia virus facilitates transmission through fomites and by long term persistence in the environment.  In spite of vaccination, the upper respiratory viruses are commonly found in multiple cat households, shelters, boarding facilities and veterinary clinics.  Feline leukemia virus (FeLV) infections occur in 1 to 2% of free roaming cats and present a very real risk of infection.  The risk of developing a vaccine-induced fibrosarcoma from FeLV vaccination is 0.1 to 0.3%, making vaccination of outdoor cats beneficial from a risk/benefit ratio.  Vaccination of strictly indoor cats is not recommended because the disease can best be controlled by removal of feline leukemia virus infected cats from the household.  The virus is fairly labile and requires close, persistent contact for effective transmission.  In multiple cat households where the cats are chronically infected with coronavirus, the likelihood of feline infectious peritonitis in young cats is about 5%. Unfortunately, cats in this type of environment develop enteric infection at an early age that precludes effective vaccination.  Exposure to Bordetella seems to be common but the prevalence of significant respiratory disease is unclear.  If Bordetella has been a significant pathogen in your area, the vaccine should be considered for cats that will be boarded or hospitalized.

 

The key to reducing the prevalence of disease in an area is to increase the number of animals vaccinated rather than frequent vaccination of a limited group.  Herd immunity studies suggest that vaccination of 80% of the population eliminated smallpox from the planet.  Some viruses such as calicivirus appear to have resistant strains of virus that are emerging.  Multivalent calicivirus vaccines may be necessary in the future.  The genetically engineered vaccine such as the canarypox vectored vaccines require two doses of vaccine for protection and may not produce high antibody titers in spite of providing good protection.

 

A major consideration in a discussion of vaccination are the adverse effects of vaccines.  Cats that have developed a vaccine-induced fibrosarcoma should never receive another adjuvanted vaccine.  The likelihood of vaccine induced autoimmune disease seems to be low in cats.

 

Consideration has been given to measuring serum neutralizing antibodies in lieu of vaccination. Panleukopenia titer of greater than 1:8, herpesvirus titers of greater than 1:2 and calicivirus titers of greater than 1:4 appear to be protective.  A major problem is the lack of standardization from one lab to the other.  Very different results are obtained from different labs.  Antibody titers against feline leukemia virus do not correlate to protection.  In the viral infections, cell mediated immunity is a key factor in protection.  There is no commercial test to evaluate specific cell mediated immunity to a particular disease.

 

A thorough discussion of the cat’s living condition combined with a knowledge of the prevalence of disease in the area are necessary for meaningful discussion of the most appropriate vaccine protocol for each cat.

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