There seems to be so much confusion on this question – even people who work in vet clinics often do not understand! How many “distemper shots” should this puppy or kitten get? Once you know the science behind it, it is actually quite simple.
There is no set number of vaccinations a puppy or kitten should have.
It all depends on the age of the pet!
Mother cats or dogs carry their own immunity, either through prior exposure to disease, or from vaccinations. When they first nurse their offspring, they pass on immunity, or antibodies, to their babies. The more immunity a mother has (ie – if she’s been appropriately vaccinated), the more antibodies she can pass on to her babies.
Once the puppies or kittens have gained this “passive immunity”, or antibodies, from mom in the first few days/weeks of life, it starts to fade. These are intended to bridge the gap between birth (where the baby has no appreciable immune system) and the time the puppy or kitten’s individual immune system is done forming.
Maternal immunity (those antibodies they got from nursing their vaccinated mother) fades over the first 6-12 weeks of the baby’s life. If mom didn’t have great immunity herself, she didn’t have much to pass on, so by 6 weeks, her offspring likely have little to no passive maternal immunity left.
Offspring of a well-vaccinated mom may have immunity that lasts as long as 12 weeks. However, individuals in the same litter can vary greatly, with some babies’ antibodies fading faster or slower than their littermates. There’s no way to tell which puppy or kitten is hanging on to that immunity longer than its littermate.
So back to the vaccination question.
The routine “distemper vaccine” covers a combination of diseases in dogs and cats. In dogs it protects against Distemper, Parvo, Adenovirus, and Parainfluenza (nothing to do with dog flu!). Hence, it’s often called a DAPP (Here’s an article that goes into detail). Cats get an FVRCP, which protects against Feline Viral Rhinotracheitis Calicivirus Panleukopenia.
Each of these vaccines must be given a minimum of twice. The first injection “primes” the immune system, getting it revved up to make antibodies, while the second injection tells the dog’s or cat’s body to actually produce the necessary immunity (in the form of antibodies.)
Why all this talk about maternal immunity then? Because maternal immunity is very good at its job!
We normally start vaccinating puppies and kittens for the distemper combination at 6-8 weeks of age. We have no idea if their maternal immunity is still going strong, or if it’s gone. If they still have a decent amount, that immunity, being very good at its job, basically negates the vaccine, rendering it ineffective. It’s like they never got it. If they have no maternal immunity, the vaccine primes the immune system and is effective.
We typically give the distemper combination vaccine every 3-4 weeks, on average, until the puppy or kitten is 16 weeks old. We have no idea at what point the maternal immunity has declined and the vaccines are taking effect. We do know that by 12 weeks maternal immunity is pretty much gone in all young animals, so the 12 week shot is almost “guaranteed” to stay there, and the 16 week shot is the final shot.
Most puppies and kittens end up getting 3-4 vaccines. I’ve had some young animals get vaccinated as often as every 2 weeks and get vaccinated for distemper 6 times! They are no more protected than the ones who got the every 4 weeks vaccines. The maternal immunity just killed off any extra shots they got.
If they got a shot after the vaccine-based immunity took effect, then THAT immunity killed off the following vaccines.
What if the puppy or kitten has no maternal immunity at 8 weeks, it’s given a shot at 8 weeks, then 12 weeks. Does it need the 16 week shot? Technically no…..but we have no way of knowing that! So we give the 16 week shot and play it safe.
Now you can answer this question: If you adopt a puppy or kitten that is 12 weeks old, and are told “it needs 3 more shots” is that true?
Nope! Again, no magic in the number of shots. It’s all about when they are given. So a 12 week old needs one more shot at 16 weeks. Furthermore, any animal over the age of 16 weeks being vaccinated for the distemper combination for the first time simply needs two shots – the “priming” shot and the “booster.”