Just want to make one comment. Without knowing what percentage of the Vermont population as a whole were vaccinated against pertussis, you can't use a statement that 90% of the cases of pertussis in Vermont were in vaccinated people to prove anything about the effectiveness of the pertussis vaccine.
Making the maths as easy as possible, Say for example that 95% of a population are vaccinated against some disease. So in 100 children, 95 vaccinated, 5 not. Then 10 of these kids get the disease - 1 who wasn't vaccinated, and 9 who were, meaning 90% of the people who came down with it were vaccinated. But get this - 20% of the unvaccinated kids got the disease, while only 10% of the vaccinated. That's still a vaccine which is effective - reducing your risk of getting the disease by a factor of 2. And the higher the propertion of vaccinated people, the higher a percentage of vaccinated people getting the disease.
There's no-one debating that the pertussis vaccination isn't as effective as you might like, but that still means that if you get it you're less likely than an unvaccinated person to get pertussis.