How would you explain the difference between dog and human vaccinations?

I see anti-vaxxers posting about dogs being over vaccinated and this is proof that humans are also over vaccinated. My gut says there is a big difference between dog and human vaccination scheduling, but I can’t find any citations at this time.

My guess is that pet vaccinations aren’t tested nearly as thoroughly as human vaccinations so the odds of them being harmful is higher. My second guess is that dogs vary in size so greatly that it’s hard to make an easy to dispense vaccine that is the right amount for all the different breeds of dogs.

Anyone have any information or theories that could be used in the argument that human vaccines are different from dog vaccines?