June 22, 2017
Back in the day, dog and cat vaccines were cut and dry, and all pets were vaccinated annually, except perhaps for very old or sick animals.
Today, the subject is much more fluid, as more information comes to light regarding duration of immunity, potential negative outcomes from vaccinating too often and adverse vaccine events.
“Vaccinology is never a black-and-white topic,” said Lauren Demos, BVMS, Hons BSc (Vet Virology), president of the American Association of Feline Practitioners. “Immunity is dependent on a variety of factors. Good data does exist to suggest that core feline vaccines can induce a DOI of at least one to three years, but individual risk factors, immune status and local laws can all be other factors to consider.”1
However, research in the form of challenge studies has shown that duration of immunity for certain viral diseases can be much longer than three years.
“If you ask immunologists and vaccine scientists, they will tell you that vaccine protection against the most common viral diseases in our small animal patients—canine distemper, canine adenovirus, canine parainfluenza, canine parvovirus and feline parvovirus-panleukopenia—lasts many years, in some cases, feline parvovirus in particular, for a lifetime after appropriate pediatric vaccination,”2 said Alice M. Wolf, DVM, Dipl. ACVIM, Dipl. ABVP, adjunct/emeritus professor in the Department of Veterinary Small Animal Clinical Sciences at Texas A&M University’s College of Veterinary Medicine. “Challenge studies post-vaccination have shown protection for at least three years in dogs and up to seven and a half years in cats. Studies assessing protection on the basis of antibody titers have shown protective levels from nine to 11 years post-vaccination in dogs.”3
For some vaccines, however, true duration of immunity is more difficult to ascertain. “Herpesvirus and calicivirus vaccines in cats are a little more challenging to assess because natural infection with these diseases does not produce sterilizing immunity, and these vaccines cannot protect better than Mother Nature,” Dr. Wolf said. “Calicivirus is a particular challenge because of the large number of serotypes and the plasticity of the virus that enables it to mutate often and rapidly. No matter how well vaccinated, some cats will still show mild clinical signs of disease and may become chronic carriers of either herpesvirus or calicivirus when exposed to pathogenic virus.”
A study commenced by the Rabies Challenge Fund (RCF) Charitable Trust nearly a decade ago to determine the duration of immunity conveyed by rabies vaccines is now complete. The goal of the study is to extend the required interval for rabies boosters to five and then to seven years. According to the most recent update published on the RCF website in April 2017, the team is reviewing the technical data from the challenge studies. W. Jean Dodds, DVM, co-trustee of the RCF, is assessing the data and will begin writing a scientific paper for publication and peer review.
If the RCF study shows a longer duration of immunity than is currently accepted, more work will need to be done before revaccination guidelines can be updated.
“I believe it is important to note that legislation has not changed, and veterinarians are bound by local and state law on how often to vaccinate for rabies,” said Heather B. Loenser, DVM, veterinary advisor, public and professional affairs for AAHA, based in Lakewood, Colo.
The vaccine guidelines published by major veterinary organizations are reviewed and updated as necessary based on current research. The present American Animal Hospital Association Canine Vaccination Guidelines recommend pediatric vaccination and revaccination one year after the pediatric series is completed, then revaccination no sooner than every three years for core vaccines. Although the guidelines have been in place for many years, Wolf said that not all veterinarians follow these recommendations.
“There are still some veterinarians who vaccinate their patients yearly with these antigens in spite of these guidelines becoming standard of care,” said Wolf, who also is chief consultant for the Veterinary Information Network. “Alternatively, some veterinarians are extending the revaccination interval after year one well beyond three years. Given the data on duration of immunity in the published literature for the core antigens, I believe that we can rely on our excellent biologic products from the major manufacturers to provide our patients with solid protection for many years beyond the three-year recommendation.”
Wolf believes that as vaccine guidelines continue to evolve and more veterinarians become comfortable with the long duration of protection afforded to their patients by modern vaccine products, recommended revaccination intervals will extend further.
The American Animal Hospital Association currently is updating its canine vaccination guidelines and plans to publish the new guidelines later this year, according to Dr. Loenser.
“They will be published in a groundbreaking online format—mobile-ready and easily updateable as new information arises,” said Loenser, who also is staff liaison for the AAHA Canine Vaccination Guidelines. “I anticipate these guidelines will prove to be invaluable to on-the-go practitioners and veterinary team members. They will also be available to the public—as all of the guidelines are—with supporting material that will explain key points of interest to pet owners.”
Dr. Demos reported that there are no plans to update the AAFP Feline Vaccination Guidelines at this time, although AAFP reviews them regularly and provides updates when new research and information is available.
“As feline medicine is constantly evolving, future updates to individual guidelines are always considered when warranted by new data,” she said.
Consumer wariness of vaccines is possibly at an all-time high, in part thanks to the internet and “Dr. Google” syndrome. Clients certainly are asking more questions than ever before, but it’s hard to say if higher numbers of clients are opting out of vaccines, as there is no way to track such data.
“Obtaining widespread statistics in veterinary medicine is difficult, but anecdotally, I have not appreciated changes in pet owner compliance regarding vaccines,” Demos said. “There’s good reason for that. Without appropriate vaccine schedules, cats can become seriously ill and even risk death. Further, zoonotic diseases such as rabies are a community-wide concern, and vaccinating companion animals is an important factor in limiting human contact with a deadly disease.”
The Association of Feline Practitioners offers several resources to help educate clients about vaccines, including a printable brochure (catvets.com/brochures) and a new cat owner website (catfriendly.com/vaccines) that can be linked to your clinic’s website or shared via your practice communications and social media.
“Depending on one’s point of view, the unprecedented amount of information that is available to the pet owners who walk into our exam rooms can either be a blessing or a curse,” Loenser said. “The days of me marching into an exam room, wielding a handful of syringes and quickly immunizing the animal without discussing the contents of these syringes with a pet owner are over.”
When talking to concerned clients about vaccine selection and frequency, Loenser keeps a simple acronym in mind—VET. This stands for validation of the client’s concerns, education about what is currently scientifically valid and tailoring vaccines for the needs of their individual pet.
“No matter the amount of misinformation the client has chosen to believe, I can do nothing for that pet if I don’t validate their efforts and work toward a goal that will allow us both to sleep well at night,” she said. “I partner with the client by discussing the patient’s risk factors, lifestyle, previous vaccination history and behavior after the vaccines, as well as educating them on the pros and cons of antibody (titer) testing. Combatting the plethora of information with empathetic validation of an owner’s concerns has allowed me to remain a trusted authority for those in my care.”
Researchers have been attempting to identify a causal relationship between vaccination and the development of invasive sarcomas ever since feline injection-site sarcoma (also known as vaccine-associated sarcomas) was first described in the early ’90s.
“Published evidence continues to accumulate that the underlying cause for VAS is chronic (months to years of) inflammation at the vaccination site induced primarily by vaccine adjuvants that is the underlying cause for malignant transformation in these locations,” Wolf said.
Wolf points out that all of the major veterinary organizations with published feline vaccination guidelines address inflammation caused by vaccine adjuvants. For instance, the specific wording in the AAFP Feline Vaccine Guidelines encourages the use of “less inflammatory (vaccine) products whenever possible.”4 According to the World Small Animal Veterinary Association Vaccination Guidelines, “non-adjuvanted vaccines should be administered to cats wherever possible.”5 Additionally, the European Advisory Board on Cat Diseases Guidelines on Prevention and Management of Feline Injection-Site Sarcoma state, “non-adjuvanted, modified-live or recombinant vaccines should be selected in preference to adjuvanted vaccines.”6
“Estimating the current incidence (of VAS) is difficult, since many factors are involved, and a national health care database doesn’t exist for veterinary patients to allow for disease surveillance,” Demos said. “More information is definitely needed to better weigh the factors involved in vaccine-associated sarcomas; it remains a hotly debated topic, and one that is difficult to research along the lines of Koch’s postulates.”
Wolf noted the difficulty in conducting epidemiologic studies of VAS in cats.
“The time between vaccine administration and detection of a VAS may be as short as four months or as long as 13 to 15 years,”7 she said. “Therefore, it takes a long time to collect enough data from enough cats with a long enough known history to say anything meaningful. In speaking with veterinarians around the country, I do think that the overall incidence of VAS is decreasing, most notably in practices where the veterinarians are now using all non-adjuvanted feline vaccines.”
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