Why Vaccinating Too Young Can Do More Harm Than Good

Why do many veterinarians like to wait until a puppy or kitten is at least 7 to 8 weeks of age prior to administering initial vaccinations? Here's why...

Puppies and kittens that nurse their mothers within the first 36 hours of life receive a healthy portion of colostrum, a fluid rich in disease-fighting antibodies (assuming the mother herself had been properly immunized prior to pregnancy). These "passive" antibodies will provide disease protection for the neonate for up to 8 weeks of age, at which time the levels of colostrum antibodies in the puppy or kitten's body will begin to taper off. By 16 weeks of age, they're usually gone altogether.

When you give a vaccine to a puppy or kitten prior to 8 weeks of age, the passive antibodies can inactivate the vaccine and render it useless. Unfortunately, because passive antibodies are used up in the process,susceptibility to disease actually increases. I've seen puppies receive vaccinations (given by well-meaning laypersons) as early as 3 weeks, with boosters given at 5 and 7 weeks of age. Not only is this practice tough on the immature immune systems of these little ones, it also depletes the stores of passive antibodies and increases susceptibility to the very diseases that the vaccines are designed to prevent. And treating a disease like canine parvo or feline rhinotracheitis is not cheap, nor is it always successful.

Ideally, puppies and kittens should receive their initial vaccines at 8 weeks of age, with boosters at 12 and 16 weeks of age. For those individuals that did not receive antibody rich colostrum (i.e strays; offspring of unvaccinated mothers, etc.), vaccines should be started at 6 weeks of age (the age at which the immune system should respond adequately to the vaccine), then again at 8, 12, and 16 weeks of age.