Vaccination plays a vital role in protecting cats from infectious diseases, some of which are potentially fatal. They can be exposed to these diseases from their environment, other pets, or even humans.
HealthforAnimals, the global animal medicines association, summarizes our role in ensuring animals are properly vaccinated: "We also have a moral obligation towards animals in our care, to prevent diseases rather than waiting until the animal gets sick, suffers and requires treatment."
Principals Guiding Vaccination Recommendations
The practice of recommending and giving vaccines on a fixed schedule with annual boosters has been widely discarded. Current recommendations are based on the philosophy of vaccinating each cat no more frequently than necessary. These recommendations take into account considerations for the efficacy and duration of immunity (DOI) of available vaccines; environmental risks and likelihood of exposure; the specific needs and risks associated with age and overall health status of different cats and cat populations; and socioeconomic limitations.
Recommendation vary for:
- Owned pets (and based on "inside only," "in and out," or "out only")
- Boarding facilities (or animals going into them)
- Community cats (feral) or TNR (Trap Neuter Return) program
Specific consideration may be required for:
- Travel plans
- Underlying disease conditions of the specific cat
- Pregnant or lactating/nursing cats
- Multi-cat households or kitten foster homes
Core vs Non-Core Vaccines
Core vaccines are ones that are considered "essential for health" and are recommended for all domestic cats, indoor or out, feral, or an owned pet. These include:
- Feline Panleukopenia (FPV or FPLV. aka Feline parvo or feline distemper)
- Feline Viral Rhinotracheitis (FHV. aka Herpes virus)
- Feline Calicivirus (FCV)
- Rabies (where the disease in endemic or required by law)
Non-core vaccines are recommended only for cats at risk of specific infection. These include:
- Feline Leukemia Virus (FeLV)
- Feline Immunodeficiency Virus (FIV)
- Chlamydia felis
- Bordetella bronchiseptica
Schedules For Vaccinations
National, international, and global vaccination guidelines by professional veterinary advisory boards are regularly updated and available for on-line viewing or download. These include:
- World Small Animal Veterinary Association (WSAVA): Guidelines for the vaccination of dogs and cats
- American Association of Feline Practitioners (AAFP) Feline Vaccination Advisory Panel Report: Feline Vaccination Guidelines
- European Advisory Board of Cat Diseases (ABCD): Vaccines and Vaccinations
- UK: The National Office of Animal Health (NOAH): Vaccination for animal health
These guides provide recommendations for kittens and adult cats. They include initial requirements to establish adequate levels of acquired immunity, along with renewal (booster) recommendations to retain it. For some infectious diseases, blood samples can be used to measure antibody levels (titers) to determine DOI. Though these tests do not provide evidence of protective immunity, some clinicians use high titer results as an indicator, along with low disease exposure risk that vaccines might be administered at a longer than usual revaccination interval. 
Types of Vaccines
Numerous types and brands of commercial vaccines are available to induce acquired immunity. These include:
- Modified-live virus (MLV or "infectious") non adjuvanted
- MLV adjuvanted
- Killed virus ("non-infectious") adjuvanted
- Killed virus non adjuvanted.
Combination vaccines that provide protection against several common viruses are also available.
Selection or use of a specific type/brand of vaccine may vary depending on the overall risk of viral infection to the specific animal in its environment, along with considerations for the time it takes to confer protection, its overall efficacy, the animal's health, and the potential risks associated with MLV vs killed, adjuvanted vs non adjuvanted, intranasal/ocular vs injection.
How Vaccines Are Given
The laws as to who may acquire and give vaccines varies in different countries. Some may only be acquired and given by a licensed Veterinarian, others by owners or caretakers.
The vaccine delivery method/route may vary. They may be given by injection, dermal application, or nasal/ocular application. Injection routes may be intra-muscular (IM) or subcutaneous (SQ). The specific injection site may vary depending on the type of vaccine (MLV vs killed) being given.
Reactions to Vaccines
Vaccines must undergo safety trials to receive licensing and are considered very safe. A very small percentage of animals may have an adverse reaction. All advisory boards mentioned above strongly endorse that the view that the benefits far outweigh the risks of not vaccinating an animal.
Just like kids, after vaccinations cats may experience mild and short-lived reactions such as poor appetite, lethargy, and fever. Any symptoms that persist for more than a day or two should be discussed with a veterinarian. Sometimes, for injected vaccines, a small, non-painful lump may form at the site where the vaccine was injected which usually disappears within four weeks.
Adverse (abnormal) reactions
The WSAVA defines adverse events as: "any side effects or unintended consequences (including lack of protection) associated with the administration of a vaccine product. They include any injury, toxicity or hypersensitivity reaction... whether or not the event can be directly attributed to the vaccine."
Rarely, a cat will have an allergic reaction to a vaccine. This may include facial itchiness, or be a generalized allergic reaction that includes vomiting, diarrhea, breathing difficulties, and extremely rarely, collapse. Should any of these occur, contact your veterinarian immediately. Anaphylactic reactions are rarely fatal if treated in a timely fashion. If allergic reaction occur, future vaccination may be amended by type or preceded by an allergy medicine.
Another uncommon reaction is a tumor at the injection site that develops months or years after vaccination. Talk to your veterinarian about any persistent lumps or swellings at injection sites.
Adverse events should be reported, whether their association with vaccination is recognized or only suspected. Veterinarians are encouraged to report any clinically significant adverse event occurring during or after administration of any licensed vaccine. The report, identifying the product, batch, animal and reaction involved, should be submitted to the manufacturer of the vaccine and to the appropriate regulatory agency.
- "HealthforAnimals guide aims to fill the void between vaccination facts and fiction | WSAVA Global Veterinary Community". www.wsava.org. Retrieved 2019-03-16.
- Day, M. J.; Horzinek, M. C.; Schultz, R. D.; Squires, R. A. (2016). "WSAVA Guidelines for the vaccination of dogs and cats". Journal of Small Animal Practice. 57 (1): E1–E45. doi:10.1111/jsap.2_12431. ISSN 1748-5827.
- "Feline Vaccination Advisory Panel Report | American Association of Feline Practitioners". catvets.com. Retrieved 2019-03-16.
- "Vaccines and vaccination – an introduction". Retrieved 2019-03-16.
- "Vaccination for animal health: an overview". NOAH (National Office of Animal Health). Retrieved 2019-03-16.
- "CVMA | Documents | Vaccination and Your Cat". www.canadianveterinarians.net. Retrieved 2019-03-16.
- "Vaccinations for Your Cat". 2013.