They are really not 8 week and 12 week shots -- those are just some of the suggested time frames to give them. As long as your dog has three combination vaccinations, spaced at least 3 weeks apart, that will give him the protection he needs until he is a year old and then he needs to do it again. Being a little over 3 weeks between boosters will not hurt (as long as he was not exposed to the diseases before immunity was set.)
There is actually a great deal of disagreement about the timing vaccines should be given to puppies. This is a quote I asked my vet about: "A study of a cross section of different puppies showed that the age at which they were able to respond to a vaccine and develop protection (become immunized) covered a wide period of time. At six weeks of age, 25% of the puppies could be immunized. At 9 weeks of age, 40% of the puppies were able to respond to the vaccine. The number increased to 60% by 16 weeks of age, and by 18 weeks, 95% of the puppies were protected by the vaccine. " So we probably vaccinate too early for the most part anyway. |