Why A Series Of Puppy Or Kitten Vaccines

Here is an explanation regarding the science behind why a puppy/kitten vaccination SERIES of shots is given:

It is all to do with maternal antibodies. If the mom is vaccinated, she passes antibodies for distemper and parvovirus in dogs or distemper and upper respiratory infections in cats to the babies in the colostrum and milk. As long as Mom’s antibodies are present (they last 6-20 weeks – no test available to determine when Mom’s antibodies disappear in the babies) the baby is protected against those communicable diseases.

However, Mom’s antibodies within the baby actually block the vaccine’s effect – ie. the vaccine does nothing; doesn’t help and doesn’t hurt. That’s why we administer a vaccination series, given starting at ~8 weeks and ending at 16-20 weeks.

In other words, if Mom passes antibodies to the babies, the first set of vaccines may not work (e.g. we’re physically injecting it but it isn’t able to stimulate the immune system for long-lasting protection because Mom’s antibodies are still present). So then we give the next set of vaccines at 12 weeks. MOST dogs/cats (but not all) have their maternal antibody levels low enough by then to be able to respond to that set of vaccines. Side note, this timing is why it’s so common to see parvovirus in a 10-11 week old puppy, e.g. the maternal antibody levels have waned enough within the baby so that they are susceptible, and the original vaccine(s) didn’t “take” because of the presence of the mom’s antibodies, but we haven’t given the 12 week vaccine yet, so the baby has no protection. Then that 12 week set of vaccines (that’s when we start Leptospirosis vaccine in puppies, as well) need a booster to create long-term protection…so that’s the 16 week set of vaccines. (Note that anytime an adult dog receives a first-time vaccination, a booster is required ~3 weeks later). Even then, if you live in an area where we see a lot of cases of parvovirus, it’s a good idea to booster at 20 weeks again, as there are some dogs who don’t have a good response to a vaccine till 16 weeks, and those dogs need a booster. Or, if you have a breed whom we have a notoriously hard time GETTING a vaccine to work (e.g. Rottweilers, pit bulls)….a booster at 20 weeks is strongly advised. Rabies vaccine is given at 16 weeks.