We get asked all the time “why does my small dog get the same size vaccine as my large dog?”
The answer? Vaccines are not based on the weight of a dog. There isn’t a “Low dose” or “High dose” of vaccines, because it’s the dogs immune system that is essentially doing all the work. The vaccine is developed with just enough components of a particular bacteria or virus to give both large and small dogs’ immune system a safe dose, where then your dog will create memory cells, so that when the immune system encounters it again it can defeat it easier.
To put it in a simpler definition, think of lighting a fire. The match is the vaccine and the wood and shrubbery is the immune system. You can light a small fire, or a large bonfire but you still only need a single match. The stronger the immune system the stronger the fire, regardless of the size of the dog.
“Why do we routinely vaccinate if my pet has memory cells?”
Because bacteria and viruses are still living organisms, they and your pets immune system evolves over time, therefore so do the vaccines. Giving your pet a safe dose of new developed diseases, so that if they were to encounter an actual infected source their immune system is already prepared to fight it.