"Dogs' and cats' immune systems mature fully at 6 months. If a modified live virus (MLV) vaccine is given after 6 months of age, it produces immunity, which is good for the life of the pet (i.e., canine distemper, parvo, feline distemper). If another MLV vaccine is given a year later, the antibodies from the first vaccine neutralize the antigens of the second vaccine and there is little or no effect. The titer is not 'boosted' nor are more memory cells induced.

"Not only are annual boosters for parvo and distemper unnecessary, they subject the pet to potential risks of allergic reactions and immune-mediated hemolytic anemia. There is no scientific documentation to back up label claims for annual administration of MLV vaccines. Puppies receive antibodies through their mothers milk. This natural protection can last 8-14 weeks. Puppies and kittens should NOT be vaccinated at LESS than 8 weeks. Maternal immunity will neutralize the vaccine and little protection (0-38%) will be produced. Vaccination at 6 weeks will, however, delay the timing of the first highly effective vaccine. Vaccinations given 2 weeks apart suppress rather than stimulate the immune system. A series of vaccinations is given starting at 8 weeks and given 3-4 weeks apart up to 16 weeks of age. Another vaccination given sometime after 6 months of age (usually at 1 year 4 months) will provide lifetime immunity."