The challenge to produce effective and safe vaccines for the prevalent infectious diseases of humans and animals has become increasingly difficult. In veterinary medicine, evidence implicating vaccines in triggering immune-mediated and other chronic disorders is compelling. While some of these problems have been traced to contaminated or poorly attenuated batches of vaccine that revert to virulence, others apparently reflect the host's genetic predisposition to react adversely upon receiving the monovalent or polyvalent products given routinely to animals. Animals of certain susceptible breeds or families appear to be at increased risk for severe and lingering adverse reactions to vaccines.

The landmark review commentary by Smith (1995) focused the attention of the veterinary profession on the advisability of current vaccine practices. Consequently, the newly recommended protocols for cats and dogs include: 1) the kitten and puppy vaccine series, followed by 2) a booster at one year of age, with 3) further boosters to be given every three years until 4) geriatric age, at which time vaccines may no longer be necessary and may be unadvisable for animals with aging or immunologic disorders. In the intervening years between adult booster vaccinations, humoral immunity can be evaluated by vaccine antibody serology as an indication of the presence of "adequate immune memory". This latter terminology is preferred over the term "protective immunity" because it is misleading to equate serum antibody titers with protection against disease.

Except where vaccination is required by law, animals that previously experienced an adverse reaction to vaccination or are at genetic or physiological risk for such reactions can have serum antibody titers measured annually instead of revaccination. Recently, this approach has been recommended more generally to assess the adequacy of immunity during the interval between routine adult booster vaccinations, in accordance with the policy advisory of giving them every three years to cats and dogs.

As polyvalent vaccines contain antigens other than the clinically important infectious disease agents, some may be unnecessary, and their use may increase the risk of adverse reactions. With Leptospira bacterins, the clinically important serovars are not contained in the currently licensed products, and the antibodies they elicit last only a few months. There have been very few clinical cases of infectious canine hepatitis from adenovirus-1 infection, although the standard polyvalent vaccines all contain adenovirus-2 to afford cross-protection. Other vaccine components, such as that for Lyme disease, may not be needed, because the disease is limited to certain geographical areas. Use of feline leukemia (FeLV) vaccines could be reserved for cats that live mostly outdoors or live both indoors and outdoors, and for catteries where new animals are introduced on a regular basis, as their efficacy is modest and they have been implicated along with rabies vaccine in producing injection-site fibrosarcomas. Overvaccination may occur with the varying state regulatory policies for rabies vaccination. As USDA licensed rabies vaccines have a 3 year duration, there is little justification for some individual states to insist on annual revaccination.

The overall risk-benefit ratio of using multiple antigen vaccines given simultaneously and repeatedly should be reexamined, although the luxury of asking such questions today is afforded only because the risk of disease has been effectively reduced by the widespread use of vaccination programs.

Measurement of vaccine antibody titers uses several techniques: Hemmagglutination inhibition (HI); serum neutralization (SN) or viral neutralization (VN); and indirect immunofluorescent antibody (IFA). Antech Diagnostics currently uses the IFA methodology for canine distemper virus (CDV) and canine parvovirus (CPV) antibody titers. An adequate vaccine immune response for both viruses is >= 1:5. Our methodology has been evaluated in 2 separate studies with paired samples (n=16) sent to the Cornell Diagnostic Laboratory. All samples having IFA titers >= 1:5 had parallel HI titers for CPV of >= 1:80 and CDV of >= 1:16, which is considered to represent substantial immunity.

Summary of published data shows:

• Olson et al (1988, 1997) state an adequate SN titer for CDV to be >= 1:16, and HI titer for CPV to be >= 1:80, basically in agreement with earlier published studies from Carmichael at Cornell.
  
• Carmichael (1997) stated that the ideal titer for CPV HI to be >= 1:320 and CDV SN to be > 1:100. He also stated that there is no point or need to booster CPV HI titers of >= 1:80 unless levels fall below 1:10 or 1:20.
  
• Hoskins (1997) agrees with Cornell as well for CPV (HI >= 1:80), and further states that a 4-fold increase in titer 3 weeks after vaccination represents significant immunity.
  
• McMillen et al (1995) studied humoral and cellular immunity in racing greyhounds given a minimal or intensive vaccination protocol and found little difference in the outcome with respect to titers or immune protection. Both protocols afforded good immunity. Their titers for successful immunization were the same as those of Cornell for CPV and CDV.
  
• Schultz (1995, 1997) states that a CPV HI titer of 1:160 and a CDV SN titer of 1:40 is adequate.
  
• Scott and Geissinger (1997) indicated adequate VN titers for 3 common feline viral diseases to be: feline panleukopenia virus (FPV) at >= 1:8; feline herpesvirus (FHV) at >= 1:2, although any titers is adequate; feline calicivirus (FCV) at >= 1:4 should be adequate.

Animals with measurable serum antibody titers are rapidly able to mount an anamnestic immune response to afford protection upon exposure.

Relatively little published information exists about the duration of immunity following vaccination. Although most veterinarians still recommend that annual booster vaccinations be given after completion of the initial vaccine series and continue in old age, an increasing number of experts advocate lengthening the interval between boosters, especially for geriatric animals. Others reason that the waning immune function of older animals should be boosted by giving vaccinations more frequently. The latter suggestion may be unnecessary and unwise, especially in light of the long term immunologic memory elicited by earlier vaccination or exposure and the likelihood of the pet having age-related diseases.

In-depth study examined the duration of serum antibody response to CPV, canine adenovirus-1 and CDV immunizations. Adequate titers against CDV were found in 83% of a large group of dogs vaccinated more than 4 years beforehand. For cats, a triple valent inactivated FPV, FHV and FCV vaccine, given in 2 doses at 8 and 12 weeks of age, produced high antibody titers against FPV for at least 6 years, and measurable titers against FHV and FCV for at least 3 and 4 years, respectively.

Please call laboratory for details on the Feline Vaccine Panel.