Dr. Eugene Shapiro of Yale University, writing in the Journal of the American Medical Association, said while there is speculation recent outbreaks of whooping cough are linked to the vaccines' waning immunity over time, there is no definitive evidence that this is the primary or sole reason for increases in reported cases of pertussis -- a highly contagious bacterial disease.
The original whole-cell pertussis vaccine DTwP, which also included vaccines against diphtheria and tetanus, was introduced for childhood immunization in the 1940s. The cellular combination pertussis vaccines DTaP replaced DTwP in the early 1990s because the whole-cell vaccine had high rates of side-effects such as fever and inflammation at the injection site.
The current DTaP uses purified components to reduce side-effects but, Shapiro said, there is not enough data on the duration of the DTaP vaccine's immunity to make any conclusions.
"There have been periodic outbreaks in the past even with the whole cell vaccine, so there is no way to know for sure that the outbreaks are linked to the accelular vaccine," Shapiro said in a statement. "There is no definitive evidence as to why there are increased outbreaks, and there may be multiple reasons."