By Fran Rotondo, BSc., DVM, DACVPM

Domestic cats, ancestors of the wildcat Felis sylvestris lybica, have been living alongside humans as far back as the Stone Age (roughly 4,000 years ago)—thousands of years after dogs were first domesticated by man at the end of the last Ice Age (approximately 11,000 years ago). It is indisputable that dogs, commonly termed “man’s best friend,” are considered more domesticated than cats. Indeed, even the tamest housecat has vestiges of its ancestral wildcat within, manifesting in those late-night moments of frenzied activity or the innate hunting instincts every cat retains.

Given this “wilder” nature, cats are often perceived as being self-sufficient and independent. This is evident in Canadian pet owner surveys, which indicate more dogs are brought in for regular healthcare visits as compared to cats. There are approximately eight million cats across Canada (versus roughly six million dogs); however, less than half of them are brought to the veterinarian for regular preventive health visits.¹

Preventive medicine and vaccination

Preventive healthcare by way of vaccination has been the single most effective means of infectious disease control in our pets. Market research has shown dogs are much more likely to receive regular vaccinations than cats. In 2022, there was an 86 per cent rate of medicalization (i.e. any preventive or therapeutic medical care) of pet dogs, compared to only 61 per cent of cats.² Cat owners do not always realize the importance of keeping their feline friends up-to-date on their immunizations, whether they are strictly indoor cats, allowed outdoors supervised, or are free-roaming. Regular preventive healthcare of cats not only ensures the health of the animal by reducing the risk of infectious diseases, but it also ensures the health and safety of their human family members by reducing the risk of zoonotic diseases.

A cornerstone of preventive care—both in human and veterinary medicine—is immunization. Routine vaccination of cats against feline panleukopenia (FPV), calicivirus (FCV), herpesvirus/rhinotracheitis (FHV-1), and rabies began in the 1970s, and all were modified-live virus (MLV) vaccines. MLV (or live attenuated) vaccines are immunogenic without the need of an adjuvant; they stimulate both humoral and cellular immunity of long duration.

Killed vaccines for rabies, FPV, FCV, and FHV-1 (FvRCP) were introduced in the 1980s, as well as feline leukemia virus (FeLV); MLV rabies vaccines were discontinued at this time and are no longer available. Killed (or inactivated) vaccines generally require an adjuvant to induce a sufficient immune response. These antigens are all part of the routine vaccination of cats to this day, although there are now non-adjuvanted recombinant rabies and FeLV vaccines for cats which have been available for more than 20 years. All FvRCP vaccines available in Canada are MLV and, therefore, are non-adjuvanted.

The shift toward using non-adjuvanted vaccines in cats in the last two decades stems from the hypothesis this would reduce the risk of chronic inflammation, which is thought to lead to the development of injection-site fibrosarcomas in genetically predisposed cats. (There is still some controversy surrounding this topic, which is beyond the scope of this article; however, there are many peer-reviewed publications that address this issue and have been cited for further reading.^3-5)

It is undeniable the vaccination of cats has greatly reduced the incidence of preventable infectious diseases in these animals, extending their lifespan and improving their overall quality of life. There are certain disease agents that are considered ubiquitous and pose a moderate to severe disease risk to all cats, while other diseases are more associated with a risky, free-roaming lifestyle. As such, experts in the field of veterinary vaccinology make the distinction between “core” and “non-core” (i.e. optional) vaccines when designing guidelines for cats. (Full vaccine guidelines are available online and provide a fantastic resource for your practice.^6-9)

Core vaccines

Core vaccines in cats include FHV-1, FCV, and FPV (FvRCP). FeLV is considered a non-core or “lifestyle” vaccine for adult cats by expert groups; however, guidelines published by the American Animal Hospital Association (AAHA) and the American Association of Feline Practitioners (AAFP) recommend all kittens receive an initial series, as this is the age at which they are most susceptible to infection. It is also possible for the lifestyle of kittens to change, even if it is originally intended for them to be kept strictly indoors.

Rabies is another vaccine that carries the caveat to administer to cats when “legally allowed/mandated or in an endemic region.” In Canada, there are some provinces with bylaws mandating pet owners have their cats, dogs, and ferrets vaccinated against rabies (e.g. Ontario), while in other provinces, there are only specific municipalities where rabies vaccination is mandatory (e.g. Winnipeg). Check your local regional requirements for rabies vaccination to ensure you are making the correct recommendations for your clients.

Guidelines for core vaccines

FvRCP

The typical protocol for FvRCP vaccination of cats is as follows: initial vaccine series at 8, 12, and 16 weeks of age; then one year later; then every three years thereafter, based on risk-benefit assessment.

The most recent AAHA/AAFP guidelines introduced the option of administering a booster six months after the initial kitten series. This is to potentially reduce the window of susceptibility in kittens that may still have maternally-derived antibodies toward the end of the kitten series (16 to 18 weeks), which could have interfered with vaccines. This extra visit also offers a bonus opportunity to consult with the cat owner on important topics, such as nutrition, weight management, parasite control, and other issues, and can also serve as the pre-surgical visit before a spay/neuter procedure.

FeLV

FeLV vaccination should be considered core in kittens (less than one year of age), where two initial vaccines (e.g. at 8 and 12 weeks of age) are followed by a booster one year later. This is to protect the kitten during the time they are most susceptible to succumbing to FeLV infection.

Unfortunately, it is all too common kittens are rehomed or surrendered to shelters once they become full-grown. This means they may start off in a low-risk lifestyle (e.g. living in a one-cat high-rise condo), but then end up living in a multi-cat household where they are given the option of going outdoors unsupervised. Vaccinating kittens against FeLV ensures protection, despite any changes to their lifestyle when they are at their most vulnerable. Once the cat is over a year of age, annual risk-benefit assessment should be performed to determine if it is at continued risk.

Rabies

There are two non-adjuvanted recombinant rabies vaccines approved for cats in Canada: one with a one-year duration of immunity and another with a three-year duration of immunity. A single dose of rabies vaccine can be given as early as 12 weeks of age. This is followed by a booster one year later, then re-vaccination, which may be annually or every three years thereafter.

Feline non-core vaccines

Vaccines are determined to be “non-core” if the disease is not prevalent in a certain geographic location, or if it is only a risk to cats with a specific lifestyle. The vaccine antigens that have been classified as being non-core in cats are Bordetella and Chlamydia, as well as FeLV in cats older than one year.

Bordetella bronchiseptica

This respiratory bacterial pathogen can cause mild illness with fever, coughing, sneezing, ocular discharge, and lymphadenopathy in cats. Since the infection generally causes only a mild disease, it is considered a non-core vaccine antigen. The vaccine may be considered as part of a control program in a multi-cat household where infection is confirmed.

Chlamydia felis

Chlamydiosis in cats can cause signs such as clear or coloured discharge from the eyes; reddened, swollen conjunctivae in one or both eyes (conjunctivitis); discharge from the nose; and sneezing. The vaccine does not completely protect the cat from infection (which is why it is classified as a non-core vaccine antigen), but it can significantly reduce the severity and likelihood of infection. The vaccine may be considered as part of a control program in households with multiple cats where infection is confirmed.

FeLV

Once cats have received their initial kitten series, including the one-year booster, a risk-benefit assessment should be conducted yearly to determine if the cat is at risk of FeLV exposure. Higher risk exists for cats that are allowed to roam outdoors freely where they could come into contact with FeLV-positive cats. FeLV can be transmitted from cat to cat via bite wounds, but it can also be transmitted simply from cats being in close contact, grooming each other, or sharing water and food bowls. There is also risk for the cat that stays indoors but lives with cats that roam freely outdoors or cats that are already known to be FeLV-positive. Cat owners that participate in fostering programs should also make sure their own cats are vaccinated against FeLV.

Designing vaccine protocols

Vaccine protocols should be designed for individual patients following an initial risk-benefit assessment based on the age, health, lifestyle, and environment of the cat. It is also important to ascertain if there are vulnerable people in the cat’s household, such as pregnant women, people undergoing cancer treatment, young children, elderly family members, or immunocompromised people. In such households, good preventive care of pets (i.e. vaccination, parasite control) will help to mitigate zoonotic disease risk. Veterinary teams should educate cat owners on the importance of annual (or even biannual) physical assessments to determine the appropriate preventive care needs of the cat and enable early detection of diseases, ensuring the health and well-being of the whole family.

Special considerations

1) Mature (seven to 10 years of age) and senior cats (i.e. older than 10)

Depending on their health status—risk-benefit analysis is even more important here—environment will play a role in this decision, as well as the general lifestyle of the cat. Things to consider when you are assessing risk may include multi-cat households, frequent boarding, and foster cats brought in regularly.

Some may argue that as cats mature their immune systems may weaken, and, since this immunosenescence naturally occurs as cats age, they may benefit from up-to-date core vaccines. Another argument is mature/senior cats may be brought to the veterinarian more often for healthcare assessments or even for hospitalization and will, therefore, be more exposed to other animals while at the veterinary clinic. Where appropriate, FCV, FHV-1, FPV, and rabies are considered core vaccines for healthy seniors.

Titer testing may be of some use to determine level of antibody against FPV and decide if vaccination is necessary or not. Antibody titers are not reliable for assessing immunity against FHV-1, FCV, FeLV, or rabies. (Detailed discussion of the use of titers falls outside the focus of this article; further information is discussed in the AAHA/AAFP feline vaccination guidelines.¹⁰)

2) Retrovirus testing

Knowing the retrovirus status of cats prior to vaccination is important. Ideally, kittens are tested for feline immunodeficiency virus (FIV) and FeLV at the time of adoption, or upon intake into a shelter or rescue. Cats with retroviral diseases (i.e. FIV, FeLV) should still receive their core vaccines, as they are at more risk of developing severe clinical disease if exposed to FPV, FHV-1, and FCV. Further, cats that are FIV-positive should still be vaccinated against FeLV, as they are immunocompromised and, thus, more susceptible to infection after exposure. Cats that are already FeLV-positive do not benefit from receiving FeLV vaccines, but should still receive core vaccines, as they are immunocompromised and will be more susceptible to clinical disease if exposed to the core viral antigens.

3) Vaccine adverse events

Vaccine reactions in cats are fairly rare. In a report of vaccine adverse events (VAEs) reported to the Canadian Food Inspection Agency’s (CFIA’s) Canadian Centre for Veterinary Biologics (CCVB) between Jan. 1, 2010, and June 30, 2014, the rates of inflammatory reactions in the current report for cats were 0.176 per 10 000 doses for pain, 1.473 for lethargy, 0.438 for fever, and 0.017 for malaise, which are lower than what was reported for dogs. The reported VAE rates for rabies vaccines were very similar to the rates for dogs (0.278 for pain, 1.969 for lethargy, 0.180 for fever, and 0.022 for malaise).¹¹

The veterinary team should inform the owner that their cat may experience mild, short-lived immune responses that may manifest as general malaise, poor appetite, lethargy, and/or fever that will resolve without treatment. Severe reactions are rare, but clients should be told to seek immediate veterinary attention if their cat begins vomiting; if they develop pruritus, hives, or facial swelling; or have difficulty breathing within a few hours of being vaccinated. Provide after-hours service information to all clients in the event of a post-vaccinal reaction requiring medical attention. (Report any and all suspected vaccine adverse events to the manufacturer, who will, in turn, report the event to the CCVB as part of their regulatory process.)

Pre-treating a cat that has had a previous mild/moderate vaccine reaction may help to mitigate the risk of a repeat VAE, but we cannot guarantee it will prevent another incident. The decision to re-vaccinate a cat that has had a VAE in the past should be made after risk-benefit assessment and with the owner’s informed consent.

Pre-treatment may involve a dose of preemptive analgesic (i.e. non-steroidal anti-inflammatory drug [NSAID]) if the cat was particularly sore after a previous vaccine or if they developed a fever. Antihistamines may be warranted if the cat exhibited signs of a classic Type 1 Hypersensitivity (vomiting, hives, pruritus, facial swelling) with previous vaccines, and may help to prevent a recurrence. In any case, pet owners should be made aware that, if the pet had a vaccine reaction in the past, they may have another one, despite pre-treatment efforts. In the event a cat has had a severe reaction in the past (i.e. anaphylactic shock) it would be advised not to vaccinate again in the future, unless the risk of disease outweighs the risk of a repeated VAE.

The value of improving cat care

The biggest challenge faced in veterinary clinics everywhere—and the main reason for the low medicalization rate of cats—is the fact that so many owners are not bringing their cats in for regular veterinary visits. It is all too common we do not see cats again for many years after their initial vaccines and spay/neuter is completed. These animals will go most of their lives without any medical attention, only to be brought in once they reach their senior years because they have developed clinical signs the owner cannot live with any longer. AAFP has resources for the veterinary team to help increase cat visits to your clinic.^12,13

There are many reasons why improving cat care is something we should all strive for. The main reason is, of course, to improve cats’ health, as well as the length and quality of their lives. The cat is the most popular pet in Canada, serving as an important family member in millions of households across the country. Keeping these felines healthy with a well-thought-out vaccination protocol helps to enhance and support the human-animal bond.

Fran Rotondo, BSc., DVM, DACVPM, is a technical services veterinarian at Boehringer Ingelheim, where she is responsible for supporting sales of veterinary products by providing technical information and assistance to veterinarians and customers. A Diplomate of the American College of Veterinary Preventive Medicine, Dr. Rotondo has an Honours Bachelor of Science degree in Microbiology from the University of Guelph (U of G). She completed her DVM at the Ontario Veterinary College (OVC).

References

¹ Cosgrove N. Canada pet ownership statistics to know in 2023: How many Canadians have pets? Pet Keen. 4 Apr 2023. https://petkeen.com/pet-ownership-statistics-canada/#Pet_Care_by_Pet_Owners

² Canadian Animal Health Institute (CAHI). “Latest Canadian pet population figures released.” CAFI press release, 22 Sept 2022. https://www.globenewswire.com/news-release/2022/09/22/2521210/0/en/Latest-Canadian-Pet-Population-Figures-Released.html (accessed 24 Apr 2023)

³ Hartmann K, Day MJ, Thiry E, et al. Feline Injection-site Sarcoma: ABCD Guidelines on Prevention and Management. J Feline Med Surg. 2015;17(7):60613. https://pubmed.ncbi.nlm.nih.gov/26101312

⁴ Graf R, Guscetti F, Welle M, et al. Feline Injection Site Sarcomas: Data from Switzerland 2009-2014. J Comp Pathol. 2018;163:1-5. https://pubmed.ncbi.nlm.nih.gov/30213367

⁵ European Advisory Board for Cat Diseases (ABCD). “Guideline for feline injection-site sarcoma.” https://www.abcdcatsvets.org/guideline-for-feline-injection-site-sarcoma (accessed 24 Apr 2023)

⁶ Day MJ, Horzinek MC, Schultz RD, Squires RA. WSAVA Guidelines for the Vaccination of Dogs and Cats. Journal of Small Animal Practice. 2016 Jan;17: E1-E45. https://wsava.org/wp-content/uploads/2020/01/WSAVA-Vaccination-Guidelines-2015.pdf

⁷ Stone AES et al. 2020 AAHA/AAFP Feline Vaccination Guidelines. JAAHA. 2020;56: 249-265. https://www.aaha.org/globalassets/02-guidelines/feline-vaccination-guidlines/resource-center/2020-aahaa-afp-feline-vaccination-guidelines.pdf

⁸ European Advisory Board for Cat Diseases (ABCD). https://www.abcdcatsvets.org/category/guidelines/general  

⁹ Cat Healthy: Vaccinations. https://www.cathealthy.ca/protocols/vaccinations

¹⁰ American Animal Hospital Association (AAHA): Serology and Diagnostics. https://www.aaha.org/aaha-guidelines/2020-aahaaafp-feline-vaccination-guidelines/serology-and-diagnostics

¹¹ Valli LJ. Suspected adverse reactions to vaccination in Canadian dogs and cats. Can Vet J. 2015;56(10):1090-1092. https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/26483587

¹² American Association of Feline Practitioner (AAFP). “Ten solutions to increase cat visits.” https://catvets.com/public/PDFs/Education/Solutions/solutionsbrochure.pdf

¹³ American Association of Feline Practitioner (AAFP) Cat Friendly Certificate Program. https://catvets.com/cfp/cat-friendly-certificate-program