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Are boosters necessary?
Scientific studies for and against

THE CONTROVERSY over whether or not annual booster vaccinations for dogs and cats are necessary continues to rumble on, following the publication of an open letter by more than thirty vets in the Veterinary Times, stating that many vaccines for life-threatening diseases last for many years and sometimes provide life-long immunity.

The vets claim that this makes the annual boosters recommended by the manufacturers of vaccines unnecessary, pointing to recent research from the USA, which claims that annual boosters might even be harmful to pets.

The veterinary surgeons’ professional body, the BSAVA, rejected the claims and warned that animals would suffer if their owners neglected regular jabs.

Both ‘sides’ in the argument point to their own chosen pieces of research that back their views. Here, OUR DOGS publishes both research documents and invites readers to make up their own minds on whether or not annual booster vaccination are necessary.

AGAINST BOOSTERS

JOURNAL of the American Animal Hospital Association 119 (March/April 2003)

Introduction

While the debate over the frequency of vaccine use has dominated both veterinary and pet owner-directed literature recently, few will debate the tremendous benefits that vaccines have brought to both veterinary and human health care. As veterinarians, it is therefore safe to say that no single achievement has had greater impact on the lives and well-being of our patients, our clients, and our ability to prevent infectious diseases than the development and ongoing improvements in companion animal vaccines.

The evolution of biologics represents a continuum of advances encompassing efficacy, safety, and usage. Early vaccines did not enjoy the same safety and efficacy profiles of currently available products, often resulting in adverse reactions or short durations of immunity (DOI). The resulting recommendations for re-vaccination reflected these product limitations, and most of the widely accepted recommendations for re-vaccination were based on a "better safe than sorry" approach because the diseases these vaccines were designed to prevent were widespread and devastating.

While the evolution of scientific knowledge has resulted in tremendous improvements in the field of vaccinology, the ultimate goal of combining 100% efficacy and 100% safety into the same vaccine product is not a reality at this time. Therefore, current knowledge supports the statement that no vaccine is always safe, no vaccine is always protective, and no vaccine is always indicated. However, the information that this statement is based on is in a constant state of flux; hence, the historical and current debate on appropriate vaccine use.

While significant efforts have been expended and realised with respect to vaccine efficacy and safety, their impact on product use (specifically vaccine protocols) has largely been ignored until recently; this despite early recommendations for less frequent re-vaccination.

Misunderstanding, misinformation, and the conservative nature of our profession have largely slowed adoption of protocols advocating decreased frequency of vaccination. Recently, however, a growing body of experts have come out in favour of defining core versus noncore vaccines and adopting triennial vaccination protocol when using core vaccines. The result has been updated vaccine guidelines from both the American Veterinary Medical Association and the American Feline Practitioners Association. While the former was general and the latter specific to the feline species, the purpose of these guidelines are to make recommendations specific to the canine species and provide additional information to both support the recommendations as well as their implementation within individual practice settings.

Task Force Recommendations Regarding the Selection and Use of Canine Vaccine Antigens
Decisions on vaccine selection and use require a balance among disease incidence and severity, vaccine efficacy (including DOI) and safety, and the health, welfare, and lifestyle of the individual animal. When taking all these variables into account, it becomes readily apparent that a blanket or generic statement encompassing the use of all vaccine products is impossible to make. However, based on the growing body of knowledge in the areas of vaccinology and immunology, general vaccine guidelines are appropriate and useful as a foundation upon which to make specific recommendations for our individual patients.

Vaccine Selection: Core (Recommended), Noncore (Optional), and Not Generally Recommended Canine Vaccines

Recommended or "core" vaccines are those that the committee believes should be administered to all puppies (dogs <6 months of age) or dogs with an unknown vaccination history.

The diseases involved have significant morbidity and mortality and are widely distributed. The committee believes this group of vaccines comprises canine distemper virus, canine parvovirus, canine adenovirus-2, and rabies virus.

Optional or "noncore" vaccines are those that the committee believes should be considered only in special circumstances because their use is more dependent on the exposure risk of the individual animal. Issues of geographic distribution and lifestyle should be considered before administering these vaccines. In addition, the diseases involved are generally self-limiting or respond readily to treatment. The committee believes this group of vaccines comprises distemper-measles virus, canine parainfluenza virus, Leptospira spp., Bordetella bronchiseptica, and Borrelia burgdorferi.

Vaccines identified as "not generally recommended" are those that the committee believes have little or no indication. The diseases involved are either of little clinical significance or respond readily to treatment. In addition, the vaccines available against these diseases have not demonstrated clinical efficacy in the prevention of disease and may produce adverse events with limited benefit. The vaccines that the committee believes fall into this category are Giardia spp., canine coronavirus, and canine adenovirus-1.

Frequency of Vaccine Use

All commercially available vaccine products have attendant vaccine protocols as defined by their manufacturers. These generally involve an initial (often puppy) series, followed by recommendations for re-vaccination (booster) at 1 year of age and annually (or less) thereafter. Regardless of product chosen, the current controversy over vaccination protocols centres on the traditional recommendations regarding re-vaccination schedules for dogs 1 year of age. The currently recommended vaccination schedules (with respect to frequency, not product choice) for dogs <1 year have not been questioned. Based on a growing body of information regarding immunology and product DOI in both animals and humans, the need for annual re-vaccination has been placed in doubt. Duration of immunity is the critical determining factor but it defies simple definition; principally, because it is derived from a complex interplay between the host’s immune response and the vaccine in question, and it is difficult to measure in an individual animal without direct challenge.

Current scientific knowledge demonstrates that DOI varies among vaccines and is influenced by vaccine type (e.g., modified live, killed, or recombinant), route of administration, and antigen content and often extends for greater than 1 year. This information is summarised in Table 2.

Supportive Information

It is beyond the scope of this Executive Summary to thoroughly discuss the extensive body of knowledge with respect to vaccinology. However, it should be recognised that certain key concepts and principles are fundamental to the understanding and critical evaluation of this report.

These include concepts pertaining to immunology, DOI, serological testing, vaccine production, adverse-event reporting, and legal implications of biological use. In the full report, the Task Force members provide a brief discussion on the implications that adopting these guidelines and recommendations bring to clinical veterinary practice.

An understanding of immunology and the immune system forms the foundation for the discipline of vaccinology and provides the veterinarian with the necessary knowledge to make an informed decision, with respect to both product and protocols. The key immunological concept that supports triennial core vaccine use is the generation of memory cells during an immune response to an antigen. This immunological memory (i.e., anamnestic response) provides

DOIs for core infectious diseases that far exceed the traditional recommendations for annual re-vaccination. This is supported by a growing body of veterinary information as well as well-developed epidemiological vigilance in human medicine that indicates immunity induced by vaccination is extremely long lasting and, in most cases, life-long. The Task Force recommendations regarding the selection and use of canine vaccines support the contention and available scientific information that, similar to human vaccine response, immunity in the canine derived from vaccination persists for years.

The issue of serologic testing to determine immunity or lack of immunity is very controversial. The issue is not one of efficacy but rather of interpretation. Since most noncore vaccines should be administered at least annually when used, there is no indication for serologic testing. Because state or provincial law sets the frequency of administration of rabies vaccines, testing is not indicated. This leaves a gray zone of serologic testing for the core vaccines of canine distemper and canine parvovirus as well as canine adenovirus.

Serologic testing is available, but there has been little standardisation of methodology allowing easy, consistent interpretations of results between or among laboratories.

In addition, there is still a lot of confusion surrounding the interpretation of antibody levels that provide less than sterile immunity but still protect from disease.

No matter how selective or careful we are in vaccinating our patients, there are and will be adverse events. Adverse events can occur for a variety of reasons, including both the
over and underuse of vaccines. These events may take on many forms including, but not limited to, local reactions or anaphylaxis secondary to vaccine administration, failure of the vaccine to provide immunity, or precipitation of an immune-mediated syndrome or other event at some point following vaccine administration. The only way that we will ever know what adverse events are occurring, or their incidence, is to more consistently report them.

This aspect of pharmacovigilence is a responsibility inherent in providing vaccinations to our patients. This same principle applies to informed consent, which is an ethical and legal requirement of biologic use.

The reality is that vaccine administration is a medical procedure and no two patients are exactly alike. This means that vaccine decisions must be approached like any other medical decision. Indications for and contra-indications to a vaccine must be considered. Risk-benefit issues also must be considered. Clients as owners or stewards must be informed and involved in the decision-making process.

Ultimately, the decision to adopt these guidelines will have a bearing on both individual and general clinical veterinary practice. While some may opine a concern for declining patient visits and the missed opportunities to provide health care, the reality is that these guidelines provide the canine veterinary practitioner with the opportunity to focus on a more comprehensive wellness program of which vaccines comprise only a small component.

These issues as well as information on the production of vaccines can be further explored by accessing the complete Task Force Report at www.aahanet.org.

Summary

The AAHA has undertaken the development of this document in an effort to inform veterinary practitioners, clarify misunderstandings held by veterinarians, and encourage practitioners to recognise that immunisation of patients is a medical procedure. As such, it is bound by the same tenets that govern the recommendation of other medical procedures —principally, that it be tailored to the needs of the individual patient. Many diseases we immunise against are ubiquitous. Many are serious and some even life threatening.

Some are of limited demographic concern given the exposure risk for each patient. These factors have all been considered in developing the AAHA Canine Vaccination Guidelines.

In the end, each veterinarian must do what he or she determines to be in the best interest of the patient. Vaccination of individual animals produces not only individual immunity but also population or herd immunity. Since we have no readily available and reliable way to determine if each patient has developed an adequate immune response, we encourage the practice philosophy of vaccinating more patients while vaccinating each patient no more than needed.

* Please visit www.aahanet.org for a complete copy of this report.

FOR BOOSTERS

The BSAVA and BVA issued this statement regarding concerns about the over-vaccination of pets.

First and foremost, vaccination has provided the single greatest contribution to the health of our pets over recent decades.

It is absolutely necessary if we want to prevent major epidemics of disease in this country and the issue raised regarding over-vaccination of pets is simply not justified.

Furthermore, as a highly trained and responsible professional, the veterinary surgeon has one priority, the health and welfare of animals that visit the practice.

As such, the profession is duty bound to adhere to the best scientific information available to them at any given time.

The Veterinary Products Committee (VPC) - an independent, expert advisory group reporting to and advising both the licensing authority and the Government – has emphasised the safety and value of vaccination, and presented data on the extremely low prevalence of adverse reactions to these products in dogs and cats.

The VPC recommended that at this time there was insufficient justification to alter current data sheet recommendations for companion animal vaccines. To date the veterinary professional bodies have seen no justification to deviate from the VPC’s advice.

Veterinary surgeons must ensure that as many animals as possible are fully protected against killer diseases such as parvovirus, hepatitis, distemper and leptospirosis and that this protection is maintained throughout their life.

The fact remains that we still do not know enough about the true duration of immunity in individual animals but we do know enough to be able to say that not all vaccines necessarily provide lifelong protection.

The degree and duration of immunity can vary greatly between different individuals and many external factors also have to be taken into account. Without actually testing the immune status of the animal for every disease, one cannot know the level of immunity it possesses.

Whilst this testing is possible it incurs extra expense to the owner and may well serve only to demonstrate that the animal does indeed require a booster vaccination. We have no problem with discussing this issue with our clients.

If, after consultation with their veterinary surgeon, a client decides that they wish their pet to have less frequent vaccinations, we are happy for the vet to do so – this represents informed consent on the part of the owner – but we see no reason to vary from the legal requirement to follow data sheet recommendations otherwise.

Given the proven safety of companion animal vaccines and in the light of the best scientific evidence presented to practitioners in this country from independent bodies such as the VPC, we see no reason to change vaccination policy at this time.

Should new information appear that proves differently, then our profession will respond accordingly.

An independent and scientifically peer reviewed study presented in the UK for the first time at the 2004 BSAVA Congress in Birmingham has produced the clearest evidence yet that routine vaccination of dogs in the UK does not increase frequency of illness.

The study – nicknamed POOCH (Practice Overview of Canine Health)1 – was carried out by the world renowned Animal Health Trust at Newmarket.

"This is completely contrary to the claims which have hit the headlines," says Dr James Wood, head of epidemiology at the Animal Health Trust. "People should understand that our research results clearly demonstrate the absence of any deleterious association between routine vaccination and signs of ill health."

The Study

The AHT’s research took the form of an epidemiological investigation to evaluate the evidence for any temporal association between vaccination and ill-health in dogs. In total, more than 9,000 postal questionnaires were sent to the owners of a randomly selected population of dogs and just over 4,000 of these were returned and analysed. No temporal association was found between vaccination and ill-health in dogs after adjusting for potential confounders, such as age.

The study population consisted of dogs that had used the services of a veterinary practice within the previous 12 months. The British veterinary practices contacted were randomly selected from a national list. Dogs were then randomly selected from the computer databases of the 28 practices that agreed to participate. On receipt of the owners’ completed questionnaires, details of the dogs’ vaccination history were confirmed with the veterinary practice.

The survey found that older dogs in general exhibit more signs of illness, including chronic lameness, stiffness and bad breath, and that frequency of these signs increases continuously with age. However, the results demonstrated that recent vaccination (within a period of 3 months) did not increase the signs of ill-health by more than 0.5% and could well actually decrease them by almost 5%.

The Facts

1. Of the 3,966 dogs assessed by the survey, 50.5% were male. Ages ranged from two weeks to 23 years (median 6 years 4 months). The demographic data for 667 non-responder dogs was similar: 57% were male, with an age range of three weeks to 20 years (median 6 years 3 months). There were 124 breed groups represented including 1076 crossbred, 348 Labrador Retrievers, 180 Jack Russell Terriers and 169 Border Collies.

Time since last vaccination ranged from one day to 17 years (median 6 months). 23% of dogs were recently vaccinated (3mo), 1% (42) were unvaccinated and 1% (42) had their vaccination status recorded as unknown. The dogs’ vaccinations were predominantly combined boosters, including components to protect against distemper virus, para-influenza virus, canine parvovirus, Leptospira interrogans (serovars canicola and icterohaemorrhagica) and infectious hepatitis. Vaccinations against Bordetella bronchiseptica or against rabies had also been administered to some dogs.The POOCH survey is to be published in a forthcoming edition of the peer-reviewed scientific journal "Vaccine".

"Vaccination and ill health in dogs: A lack of temporal association and evidence of equivalence", D.S. Edwards, W.E. Henley, E.R. Ely, J.L.N. Wood, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk, UK, CB8 7UU

2. The Animal Health Trust is a registered charity committed to improving the prevention, diagnosis and treatment of injuries and diseases which affect companion animals. Based in Newmarket, Suffolk, the Trust was established in 1942 and currently employs more than 200 scientists, veterinary surgeons and support workers.

The National Office of Animal Health was formed on 1st January 1986 to represent the UK companies which research, develop, manufacture and market licensed animal health products. The association now has 33 corporate members and 14 associate members. In 2002, NOAH’s members accounted for well over 90 per cent of the £389 million UK animal health market.

3. The study was funded by members of the National Office of Animal Health (NOAH), the trade association for the manufacturers of licensed animal medicines, to properly investigate the safety of routine vaccination in the UK canine population.

NOAH submitted a proposal for a scientifically valid study, but AHT stressed that they were prepared to undertake the project only on the clear contractual understanding that the work would be completely independent and that NOAH could not influence either the outcome or the eventual publication of the results.