What will happen if my dog doesn't get his booster?

If you tell me their age I can give you some better information. If they are under 16 weeks of age then they absolutely need more boosters, as their immune system will be naive, thus they will be at risk of developing deadly diseases, of the most common which are distemper and parvo, depending on where you live. The good news is that you should booster puppy vaccines really every 3-4 weeks, so you are still in a good spot in terms of the time frame. Puppies get a natural immunity to things we vaccinate for from their mothers. This immunity is usually gone by about 16 weeks of age. What this means is that we give puppy vaccines at 3 week intervals, until the puppy is 16 weeks of age. The reason we do this is because their mom's immunity will eventually wear off, however this is so variable between dogs. It can start to wear off as early as 9 weeks. So, what we try and do is frequently vaccinate them until we know for sure their mom's immunity is gone, and thus the vaccine we are giving will become their immunity. Puppy boosters aren't really "boostering" the vaccine that was given previously. They are being given frequently until they provide the dog with appropriate immunity to untreatable (or lifethreatening) diseases. The first vaccines your puppies received were most likely destroyed by the immunity they received from their mom. This is exactly how we want immunity to work, but for example say you only get your puppies one vaccine while they still had their mom's immunity, well, once mom's immunity is gone, without any additional vaccines, they are at a high risk for catching something like parvo, as they haven't created any antibodies to it. Now, if your puppies are older than 16 weeks, that can be a bit different, so let me know.