While vaccinations can provide health protection against certain diseases, there is no guarantee that every vaccine will be effective, that the animal vaccinated will respond appropriately, or that the animal being vaccinated will not have a local or systemic adverse reaction, sometimes life-threatening, or vaccinosis, an on-going compromise of the immune system.
The veterinary medical association divided vaccines into three groups: CORE vaccines (those that are strongly recommended for health protection; think of trunk of a tree) those that are NON-CORE (think of branches on a tree), and those that are HIGH RISK, LOW in EFFICACY, or NOT RECOMMENDED (think of tree leaves that fall off annually). The core vaccines that are most highly recommended because they might provide protection against life-compromising or threatening diseases, also tend to be the most effective and have lower risk of causing adverse reactions. Core vaccines include: for dogs, Parvo, Distemper and perhaps adenovirus 2 (CAV-2); for cats, Panleukopenia vaccine; and for horses, Tetanus, Eastern/Western Encephalomyelitis, and West Nile Virus.
Rabies is a core vaccine for all species, because of human epidemiological concerns as well as rabies being a life threatening disease. Rabies is a highly effective vaccine and is the only required vaccine in the states of Oregon and Washington. The rabies vaccine in these states is given every three years after the initial one-year vaccine. All other vaccines are recommendations, not requirements, to support an animal’s health.
Vaccines should not be given all at once. To minimize the chance of having adverse vaccine reactions, give only monovalent vaccines (protection against only one disease in one injection) instead of polyvalent vaccines (those which are for multiple diseases in one shot) and space each vaccination at least three weeks apart. Also for cats especially, seek non-adjuvanted vaccines as they will be less likely to induce what sometimes are very severe vaccine reactions in this species.
It was in 1978 that Ron Schultz and Fred Scott at Cornell first recommended triennial vaccination [Vet Clin N Am 8(4):755-768, 1978]. It has taken 25 years for this recommendation of vaccinating every three years instead of annually to be adopted by veterinary scientists, industry, and mainstream veterinary medicine! There have been numerous studies, more in cats and dogs than in other species, which show that immunity from many core vaccines can last over 5 years. No cat should ever be given the same vaccination at an interval of less than three years. Many vaccines are ineffective or low in conferring any protection (such as FELV in cats, Bordetella in dogs). According to the American Association of Feline Practitioners (AAFP), the feline leukemia (FeLV) vaccine should not be given after the cat is one (1) year of age. Also the FeLV vaccine is the one most highly associated with inducing sarcoma, a highly aggressive cancer, at the vaccine site.
I have attached information / charts on the core vaccines and minimum duration of immunity of vaccines for dogs and cats. The charts on canine and feline vaccinations are from the American Animal Hospital Association (AAHA) Canine Vaccine Task Force and the AAFP. The revised AAHA Canine Guidelines and revised AAFP Feline Guidelines were published 2006. New updates came out in 2012.
Attached is information from the American Association of Equine Practitioners (AAEP) website on vaccinations. I have highlighted in blue certain sections: the vaccine interval and muscle recommendations, the recommendation to use monovalent vaccines, and time interval between vaccinations. I mentioned the recommended core-vaccines for horses above. The AAEP recognizes the following as high risk-based vaccines; that means, your horse has a higher chance of having an adverse reaction from the following vaccines: Anthrax, Botulism, Equine herpesvirus (Rhinopneumonitis), Equine Viral Arteritis, Equine Influenza, Potomac Horse Fever, Rotaviral Diarrhea, Strangles. Also, Cornell University measures vaccine titers for horses for some vaccinations.