Dilemmas over feline vaccination continue to pose challenges for the profession. Failing to act to embrace extended duration of immunity protocols sets the foundation for accusations of profiting from vaccines at the potential expense of patients.
Yet clinicians are also bound by the information provided in vaccine datasheets and deviation constitutes “off-label” use, with all the legal problems that involves.
Guidelines
A number of guidelines have been produced by the WSAVA and The American Association of Feline Practitioners (AAFP).1,2 Although there are recommendations that are common to both organisations, there is not agreement on basic protocols around core feline vaccines – with the AAFP recommending a six week start followed by repeat doses every 3-4 weeks to 16 weeks; while WSAVA recommends an 8-9 week start, a second dose after 3-4 weeks and a final dose at 16 weeks or over.
Of course, the pressure to follow published guidelines is difficult to resist, yet the profession is still bound by vaccine SPCs (the summary of product characteristics) unless they use products off-label with all the provisos that entails.
It is also difficult to explain to owners when their individual cat falls victim to disease because immunity declined during an extended duration of immunity protocol, that their pet is one of the “unlucky” animals that deviated from the norm.
Protection and immunity
The protection offered by some feline vaccines is less clear cut than with canine vaccines. Some researchers believe that any discernible titre indicates protection and some cats with undetectable titres have shown a serological response, termed an amnaestic response, in the face of challenge.3
Paul Burr of BioBest Laboratories says: “The interpretation of data is less straightforward as the somewhat sketchy data for what a protective titre is in dogs is virtually non-existent for cats. Some recent papers have taken a view that any amnaestic response documents protective levels of immunity but they have presented no evidence to back this up from a virulent challenge model.
“I would tend to take a view that cats which have shown an amnaestic response in such studies have benefited from boosting by having their immunity levels topped up. For both cats and dogs, the data from serological studies have not changed in the last 20 years; however, the fashionable interpretation for the data has changed away from vaccination.
“For calicivirus, interpretation is further complicated in that neutralisation tests document immunity to the strain of virus used in the test, not all caliciviruses. Therefore a cat with a high titre to a particular calicivirus, whether by vaccination or natural infection, is not necessarily immune to all calicivirus.”
This is all highly relevant. Feline calicivirus poses problems as there are multiple strains and prevalence of infection remains high, despite vaccination. In 2008, researchers identified that antisera raised against newer strains of calicivirus neutralised a greater proportion of field isolates.4 It’s also been suggested that vaccine-induced immune pressure may drive antigenic shift of FCV.5
There are reports of virulent systemic disease in Europe and North America caused by highly virulent strains of FCV and although some vaccine protection has been demonstrated experimentally, this does not hold up under field conditions.1
Immunity to Feline Herpesvirus (FHV) may last longer than a year but several US studies have shown that 30% of vaccinated cats have undetectable titre.3 Professor Tim Gruffydd-Jones, speaking at the 2009 WSAVA congress, recognised that experimental studies “provide compelling evidence that immunity lasts at least three years and probably considerably longer in the majority of cats”. But he also recommended that FHV vaccination should be given annually to provide minimum levels of protection and include cats that respond less effectively. This is in contrast to some of the published guidelines.
The WSAVA guidelines also point out that FHV vaccine cannot protect against infection by virulent virus which can become latent and then reactivate at times of stress, leading to clinical signs and active virus shedding.1
Feline Infectious Enteritis (panleucopaenia) has been largely a success story, with some countries rarely reporting the disease since vaccination was widely adopted and seven years and beyond duration of immunity reported in challenge and serology studies1,3.
The disease can, however, still present a problem in the UK, particularly in rescue shelters and the Feline Advisory Bureau recommends that all cats receive vaccination and regular boosters, including indoor cats6.
Vaccine reactions
Sarcomas are obviously the big concern in terms of adverse effects. Some large studies have suggested that the incidence of vaccine associated sarcomas is around 0.2-1/10,000 vaccinations.3 As well as an apparent association with FeLV and rabies vaccines, other vaccine components may be involved.
Professor Michael Day’s study compared adjuvanted vaccines with non-adjuvanted vaccines and found greater tissue reaction when adjuvanted vaccines were used, as well as accumulation of residual adjuvant in marcophages two months after vaccination.7
Although no neoplastic or preneoplastic changes were detected, Professor Day observed, “If tissue inflammation can act as a potential trigger for neoplastic transformation of mesenchymal tissue, then this effect may have relevance to the risk of different vaccines inducing sarcoma.”
Professor David Argyle reported at the WSAVA congress in 2008 that some rabies and FeLV vaccines will produce post-vaccination lumps in 100% of cats vaccinated.8 Most of these resolve over 2-3 months, in contrast to vaccine associated sarcomas which usually do not occur until three months after vaccination.
Others report sarcoma development within 3-12 months post vaccination, but it can be delayed up to three years.9 The recommendation is usually that post-vaccination lumps should be removed if still present at three months or if they grow beyond 2cm before three months. There are anecdotal reports of post-vaccination lumps being removed much earlier than this in practice, probably prompted by fear over the aggressive nature of the tumours when they do occur.
At a more basic level, it is worth keeping in mind that live modified vaccines retain pathogenic potential. Accidental aerosolisation of vaccine or ingestion of vaccine deposited on skin can result in disease.1 The classic scenario is a litter of squirming kittens brought in by a breeder in a single basket, so it is worth taking extra care in these types of situations.
Choosing a vaccine protocol
It is becoming ever more critical to develop a vaccine protocol that can be justified and substantiated but is that as easy as it sounds?
Mark Riggs of Merial believes not: “I think many cat-owners would be surprised to learn that it is not veterinary science alone that drives the protocol decision. Vets are between a rock and a hard place.
“What does the VMD mean when it comes to risk/benefit analysis? Where does the buck stop if guidelines are used as surely they were intended – for guidance, not as mandates? I find that when vets call us to discuss what our SPCs have to say with regard to a specific case, the outcome is usually that good veterinary science and, dare I say it, common sense, prevails.”
According to the latest Fort Dodge report, “Clients taking up vaccination and other preventive health products and services will tend to remain with the practice and contribute more to the practice’s finances and growth.”10
Vaccination is no longer the quick “catch-up” appointment it has been in the past. If our clients with vaccinated pets start to feel disenfranchised or short-changed, their departure could be catastrophic.
Taking the time to make the necessary explanations to support a vaccine protocol recommendation may play havoc with time management but it may well underpin the future success of the practice.
- WSAVA Guidelines for the vaccination of Dogs and Cats: www.wsava.org/PDF/Misc/ VGG_09_2007.pdf.
- AAFP 2006 Feline Vaccine Advisory Panel Report: www.catvets.com/professionals/… ublications/?Id=176.
- Gruffydd Jones, T. As quoted at 34th WSAVA Congress 2009, Brazil: Review of Vaccination Protocols for Cats.
- Addie, D., Poulet, H. et al (2008) Ability of antibodies to two new caliciviral vaccine strains to neutralise feline calicivirus isolates from the UK. Veterinary Record 163: 355-357. 5
- Poulet, H. et al (2008) Efficacy of a bivalent inactivated non-adjuvanted feline calicivirus vaccine: Relation between in vitro cross-neutralisation and heteralogous protection in vivo. Vaccine doi:10.1016/j.vaccine.2008.04.082.
- FAB Information Sheet: www.fabcats.org/owners/feline_… o.html.
- Day, M. J. et al (2007) A kinetic study of histopathological changes in the subcutis of cats injected with non-adjuvanted and adjuvanted multi-component vaccines. Vaccine doi:10.1016/j.vaccine.2007.02.049.
- Argyle, D. 33rd WSAVA Congress 2008, Decision making in feline cancer patients.
- Maudlin, D. WSAVA Congress 2001, Vaccine-associated sarcomas in the cat.
- Fort Dodge Q4 2009 Report.
