We were using DTwP 25 years ago and our Pertussis tests were not as sophisticated as they are today. That said, the DTaP vaccine does work to a degree as is evidenced in Japan, the USA, the UK, Canada, and dozens of other developed countries using DTaP with lower incidences of WC. Something is not working here though. Maybe its our climate, and the vaccine dies in our system before we can build appropriate antibodies due to that. That is the question that needs answering.
And all the figures are on the World Health Organisation page I liked to earlier.

