Natural infection of B. Pertussis uses ACT to colonize the lungs. This colonization is important as the body will remember it if re-infected not to mention ACT allows the B. Pertussis Toxin to clear the lungs. Two vital components of disease control which is exactly why a healthy host is able to beat infection with out any serious longterm effects and also gains 20 years of immunity and less complications if any in the future.
The vaccine lacks ACT. Pubmed studies have even shown that this component is lacking in the current vaccine and would be a great addition. Either cost, ignorance, biochemically unable to add or simply not considered are some of the possible reasons. Your looking at several hundred millions to make a vaccine, Phase I, II, III trials would take years, blah blah blah.
If ACT is not there the recently vaccinated will be unable to clear the infection from their lungs and become either sympomatic or asymptomatic carries of infection as the CDC acknowledges.
It gets even worse than that with the pertussis vax and the ACT issue.
Vaxing with the current vax makes the vaxed UNABLE to be immune to ACT compared to the unvaxed:
Of particular interest is the lack of a significant ACT antibody response in children for whom the DTP or DTaP vaccines failed. This induced tolerance is intriguing and may be due to the phenomenon called “original antigenic sin” . In this phenomenon, a child responds at initial exposure to all presented epitopes of the infecting agent or vaccine. With repeated exposure when older, the child responds preferentially to those epitopes shared with the original infecting agent or vaccine and can be expected to have responses to new epitopes of the infecting agent that are less marked than normal.
Also (and this is a totally different issue):