A number of factors will influence any animal's response to a vaccine. There are things that you can do at home to maximize the benefit of the vaccines your pet receives.
Stress: Acute stress causes release of adrenaline, which suppresses the immune response. Chronic stress causes release of cortisol (cortisone), which is also immunosuppressive at high levels. Cortisone can cause latent infections to become active, and can cause what might otherwise be a transient infection to become permanent. An example of this is a latent herpes infection in a cat (or cold sores in people, for that matter) which might become active when the cat is stressed. It is easy to think of what physically or emotionally stresses pets severe weather (temperature, humidity), travel, excessive handling or grooming, shows, overcrowding, trauma, illness, pregnancy, boarding, premature weaning, and even general anesthesia.
Age: Maternal antibodies are meant to protect kittens and puppies from disease but can interfere with vaccination and the pet's own immune response. The younger a kitten or puppy is at the time of an infection the greater the risk of severe or chronic illness, or death. There is also age-related resistance, such as to feline leukemia virus. Cats under 16 weeks are most susceptible, while those over a year of age rarely become permanently infected. In elderly patients the immune responses decline. The number of T and B cells declines. Other cells become less responsive to signals that would ordinarily make them more active, like interferon.
Husbandry: High population density exposes pets to more infectious agents. The same is true if there is poor sanitation, or poor ventilation in the case of kennel cough and feline upper respiratory diseases. As we saw a minute ago, high population density also causes social stresses, further compromising the immune system. Line breeding allows perpetuation of some genetic immune system defects.
Nutrition: Nutrition plays a vital role in immunity. We have recognised the effects of many nutrients on the immune system, mostly by exploring what happens in cases of deficiency. The following nutrients have been found to be very important in the development of a normal immune response:
Polyunsaturated fatty acids
B vitamins (B12, folic acid)
Many of these nutrients act as antioxidants, protecting immune cells from oxidative damage. It has been shown that puppies receiving antioxidant supplementation have a much higher level of antibody production after vaccination than unsupplemented puppies. We could be taking advantage of this known response by supplementing all puppies and kittens with an antioxidant during the period when they are receiving their initial vaccinations.
Exercise: regular, moderate exercise enhances immune response. Strenuous intermittent exercise result in oxidative damage to the cells and increases susceptibility to infections.
Severe trauma results in immunodeficiency from the massive release of corticosteroids, prostaglandins and suppressive active peptide.
Concurrent illness may impair immune response.
Drug treatment may blunt the ability of the body to respond properly to immune challenge. Drugs like cortisone, cancer chemotherapy drugs, and even some antibiotics can have this effect.