When we talk about the resurgence of childhood illnesses, we tend to focus on vaccine-resistant people as the primary cause. And it's true that a large population of un-vaccinated kids can give a disease like whooping cough a foothold in a community, and allow it to spread to kids who haven't been vaccinated yet or who can't be vaccinated for various medical reasons. But there's another facet to this story, as well. Some of the strains of bacteria that cause whooping cough are also resistant to the vaccine. Those strains have been found in Japan, France, and Finland. Last week, The New England Journal of Medicine reported on 12 cases of vaccine-resistant whooping cough in Philadelphia.