Government oversight and regulation of vaccines for pets are performed by the United States Department of Agriculture (USDA).
This means that manufacturers of vaccines must adhere to rules and regulations established by the USDA in creating safe and effective vaccines that do what manufacturers claim they do. This includes quality control monitoring by the USDA.
There are multiple large pharmaceutical companies, which allows for a healthy amount of competition to assure constant refining and improvement of vaccines, as no company wants to be outdone by the other.
So far in our US market, I believe this has helped produce pet vaccines that the majority of veterinarians consider to be very safe and efficacious.