Duration of immunity in cats after vaccination or naturally acquired infection

Feline vaccines

Many of the decisions regarding the vaccination of cats relate to the animal’s lifestyle. Vaccination requirements for the solitary indoor cat are very different than those for feral or free-roaming cats. Core vaccines include those directed against feline herpesvirus, feline parvovirus, and feline caliciviruses. Other important vaccines include the mandated rabies vaccination and also vaccination against feline leukemia. One significant issue with respect to feline vaccination is the development of injection site sarcomas. Although the prevalence of these is low and should not inhibit the use of vaccines, they are impossible to predict and very difficult to treat.

Duration of immunity induced by companion animal vaccines

Concerns about possible adverse effects from annual vaccination have prompted the reanalysis of vaccine protocols for cats and dogs. In the last decade, several veterinary advisory groups have published protocols that recommend extended revaccination intervals for certain ‘core’ vaccines. In addition, practicing veterinarians have been asked to consider vaccination as an individualized medical procedure, based on an analysis of risks and benefits for each vaccine in an individual animal. The calls for extended revaccination intervals prompted considerable debate in USA and internationally. Areas of concern include the amount of evidence to support prolonged immunity from various vaccines, the risk of poor responses in individual animals and the possible effects on population immunity. This review examines how the duration of immunity (DOI) to a vaccine is established in animals and humans. It reviews factors that can affect the DOI in an individual animal, including the types of immune defenses stimulated by the pathogen, and the vaccine, host factors such as age and the level of exposure to the pathogen. In addition, it examines DOI studies that were published for canine and feline core vaccines.

Feline herpesvirus 1 and feline calicivirus infections in a heterogeneous cat population of a rescue shelter

Feline herpesvirus 1 (FeHV-1) and feline calicivirus (FCV), associated with upper respiratory tract disease, are highly prevalent in cats worldwide. With the aim to investigate the importance of feline respiratory viruses in a heterogeneous population of cats, samples were taken in a rescue shelter in Liège, Belgium, between March 2005 and August 2006. Reverse transcription polymerase chain reaction (RT-PCR) and polymerase chain reaction (PCR) were performed to diagnose FCV and FeHV-1 infection in the sampled cats. The prevalence rate (33.1%) was higher for FCV than for FeHV-1 (20.1%) whereas prevalence rate of co-infection with both viruses was 10%. Gingivitis was more common in FCV infections (odds ratio (OR)=2.83) whereas respiratory signs were more often observed with FeHV-1 infections. The average age was significantly higher in FCV positive cats (38 months) than in FeHV-1 positive cats (29.9 months). The second and the fourth quarters of the year and the two first quarters were significantly more at risk than the others in the case of FeHV-1 and FCV infection, respectively. Age was found to be a confounding factor. High prevalence of both infections strengthens the importance of applying hygienic and preventive measures in rescue shelters where cats with an unknown status of vaccination are introduced.

Alternative early life vaccination programs for companion animals

An experimental challenge study of multicomponent vaccination of kittens is reported. Seven-to-nine week old, specific pathogen-free kittens received two injections (4 weeks apart) of non-adjuvanted, multicomponent vaccine formulated at the minimum protective dose. Kittens were challenged at 4 weeks or 1 year post-vaccination with individual infectious agents. Vaccination induced complete protection against challenge from feline parvovirus on both occasions, but at 1 year, the protection against feline herpesvirus, feline calicivirus and Chlamydophila felis was not as strong as 4 weeks after vaccination. This demonstration of a decline in protective immunity at the normal time of administration of the first booster vaccine suggests that earlier administration of this booster (at 4-6 months of age) may provide better protection. The effect of maternally derived antibody (MDA) on kitten vaccination was determined by conducting an identical experiment but with kittens born to queens vaccinated during pregnancy. Serum antibody titres to specific vaccine components were measured in these kittens on day 0 (time of first vaccination), day 28 (time of second vaccination) and day 42. There was heterogeneity in transfer of MDA to kittens within a litter, and between litters. MDA may neutralize the serological response of kittens on the first, and occasionally the second, occasion of vaccination when vaccination is performed at 8 and 12 weeks of age. This finding underpins recent recommendations that the final vaccination in the primary series be administered at 16 weeks of age.

A kinetic study of histopathological changes in the subcutis of cats injected with non-adjuvanted and adjuvanted multi-component vaccines

The aim of this study was to investigate the subcutaneous tissue response to administration of a single dose of multi-component vaccine in the cat. Three groups of 15 cats were injected with one of three vaccine products with saline as a negative control. Cats in group A received non-adjuvanted vaccine; cats in group B received vaccine with a lipid-based adjuvant; whilst those in group C were vaccinated with a product adjuvanted with an alum-Quil A mixture. The vaccine and saline injection sites were sampled on days 7, 21 and 62 post-vaccination. Biopsies of these vaccine sites were examined qualitatively and scored semi-quantitatively for a series of parameters related to aspects of the inflammatory and tissue repair responses. These data were analysed statistically, including by principal component analysis. At all three time points of the experiment, there was significantly less inflammation associated with administration of non-adjuvanted vaccine (p=0.000). Although there was evidence of tissue repair by day 62 in all groups, those cats receiving adjuvanted vaccines had evidence of residual adjuvant material accumulated within macrophages at this late time point. The severity of tissue reactions may vary significantly in response to vaccines which include adjuvants or are non-adjuvanted.

Response of feral cats to vaccination at the time of neutering

OBJECTIVE

To determine whether administration of inactivated virus or modified-live virus (MLV) vaccines to feral cats at the time of neutering induces protective serum antiviral antibody titers.

DESIGN

Prospective study.

ANIMALS

61 feral cats included in a trap-neuter-return program in Florida.

PROCEDURES

Each cat received vaccines against feline panleukopenia virus (FPV), feline herpes virus (FHV), feline calicivirus (FCV), FeLV, and rabies virus (RV). Immediately on completion of surgery, vaccines that contained inactivated RV and FeLV antigens and either MLV or inactivated FPV, FHV, and FCV antigens were administered. Titers of antiviral antibodies (except those against FeLV) were assessed in serum samples obtained immediately prior to surgery and approximately 10 weeks later.

RESULTS

Prior to vaccination, some of the cats had protective serum antibody titers against FPV (33%), FHV (21%), FCV (64%), and RV (3%). Following vaccination, the overall proportion of cats with protective serum antiviral antibody titers increased (FPV [90%], FHV [56%], FCV [93%], and RV [98%]). With the exception of the FHV vaccine, there were no differences in the proportions of cats protected with inactivated virus versus MLV vaccines.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that exposure to FPV, FHV, and FCV is common among feral cats and that a high proportion of cats are susceptible to RV infection. Feral cats appeared to have an excellent immune response following vaccination at the time of neutering. Incorporation of vaccination into trap-neuter-return programs is likely to protect the health of individual cats and possibly reduce the disease burden in the community.

Serological testing--an alternative to boosters?

The issue of the duration of immunity, particularly for the modified live viral components of veterinary vaccines, has been a significant part of the recent vaccination debate. One manufacturer has increased the recommended booster interval for these components to 3 years give name and another now states 'up to 4 years' immunity. There remain many unanswered questions regarding this duration of immunity (DOI). Studies suitable for data sheet claims are time consuming and costly and can only be performed in laboratory dogs under tightly controlled conditions. Evidence from rabies serology testing in the UK shows that the response of individual animals to routine vaccination is highly variable. Much of the published field evidence on the persistence of antibody titres originates from North America, where vaccination strategies and reservoir species differ from Europe. Quantifying the effect of exposure to field virus on the maintenance of immunity in these studies is impossible, and little is known of the circulation of virus in unvaccinated dogs and wild mammals throughout Europe. If owners or vets are concerned about revaccination one option is to assess the need for each booster by performing a blood test. There is some published evidence of the relationship between antibody titres and protective immunity, and tests are available to measure responses to individual viral components of the routine canine and feline vaccines. It must be remembered that most commercial tests to assess immunity only measure antibodies, which are only one aspect of the immune response to vaccination. It is therefore possible that animals without or with low antibody titres are in fact protected. Serological tests are an option if owners are unwilling to have their animal boostered without evidence that it is needed. However, the cost of these tests is likely to exceed that of booster vaccination for the foreseeable future.