It is very important to vaccinate young animals. It you vaccinate too early the vaccines are useless because the maternal antibodies that the puppies receive in the colostrum render the vaccine useless. If you vaccinate too late you are risking exposing the animal to disease after the maternal antibodies are no longer protecting the puppy. It is important to consult your veterinarian about appropriate timing of vaccinations in your location. In many areas the law demands that you have you animal vaccinated for rabies. If your animal bites someone it may be euthanized if you are not up-to-date with your rabies vaccine. Some vaccines are considered non-core, like leptospirosis and giardia and can be given to animal depending on their individual risk factors. For example, a veterinarian may recommend that a farm dog that drinks out of ponds be vaccinated for lepto but may not recommend this for a city dog that is only walked on leash around the block.
Many vaccines are beginning to be labelled for 3 year usage so you can check with your veterinarian if a 3 year schedule is appropriate for your pet.
In specific instances, like the vaccine reaction described above, it is riskier to the animal's life to vaccinate than it would be to contract the disease and the vet may recommend to avoid vaccinations entirely.
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