The same vaccine dose is recommended regardless of size of the dog. The premise is that the immune system response is the same, regardless of size. New research suggests this may not be true and that half doses of the distemper/parvovirus vaccine may be appropriate for small breed dogs. This is important because the smaller dose may reduce the risk of vaccine side effects in small dogs.
In a pilot study conducted by Dr. Jean Dodds, 13 adult small breed dogs between the ages of 3 and 9 years and weighing 12 pounds or less were evaluated for the serum antibody titer response following the administration of half doses of the distemper/parvovirus vaccine. Titer levels at 4 weeks and 6 months after vaccine administration were elevated compared to pre-vaccine administration, reflecting immunity in all of the dogs. A larger study enrolling more dogs may be required to verify these results. To read the full study, visit http://drjeandoddspethealthresource.tumblr.com/post/137503224896/half-dose-vaccine-small-dog-vaccine-study#.VqJv3PkrKUl
These findings are important because vaccines are known to cause adverse events, especially in smaller dogs. The ability to administer a half dose MAY reduce the risk of these adverse reactions. More research is required to determine if the incidence of adverse reactions is indeed less when half doses are given, if even a smaller vaccine dose may be effective in small breed dogs, and at what adult size is the half dose no longer adequate. We applaud Dr. Dodds for her commitment to studying the best practices for vaccine administration to our pets!