They know it can’t be polio since the children were all vaccinated for it. What a stupid thing to say. It’s like doctors these days are selected from some religious background that forbids healthy scientific skepticism.
He didn't say that, exactly. He said they know the disease wasn't polio, AND the children were vaccinated. They might have learned the first fact by testing the children's blood for the pathogen that causes polio.
The chicken pox vaccine actually gave my daughter the chicken pox.
Failure to develop antibodies against a disease is found in other types of vaccinations. For example, I did not respond to the Hep B series. A son of a friend had measles even though he had been vaccinated.