BOSTON — The efficacy of the diphtheria and tetanus
toxoids and acellular pertussis vaccine wanes as much as 40% per year after the
fifth dose, according to data presented here at the IDSA 49th Annual Meeting.
“Acellular vaccines appeared to provide less
protection than the whole-cell vaccines they replaced, and their effectiveness
may have waned substantially over time,” Roger Baxter, MD, and
colleagues from Kaiser Permanente, said.
The data were taken from three separate case-control
studies among members of Kaiser Permanente Northern California from 2006 to
2010, which is when California began experiencing a pertussis outbreak.
Researchers confirmed pertussis using polymerase chain reaction and assessed
the risk for a positive pertussis test in relation to days elapsed since the
fifth dose of DTaP and whether the child had up-to-date vaccinations.
“The efficacy of the fifth dose of DTaP wanes by
more than 40% per year,” Baxter told Infectious Diseases in
He said the study data suggested that the acellular
pertussis vaccines offer less protection than whole-cell vaccines, which he
attributed to the mix of proteins in the acellular version of the vaccine.
However, because of the reputation the whole-cell vaccines gained as
potentially harmful, it is unlikely that the acellular version would ever be
The acellular vaccines could be partially at fault for
the outbreak in California, but vaccination makes a difference, Baxter said. In
his study, those “children who were not up-to-date were twice more likely
to have their pertussis than those children who were up-to-date.”
The researchers concluded that more education is needed
about vaccine refusal, and Baxter said tetanus-diphtheria-pertussis vaccine was
moderately effective in boosting protection.
Disclosure: Dr. Baxter reports receiving research
grants from Sanofi-Pasteur, Merck, GlaxoSmithKline, MedImmune, Novartis and
For more information:
- Baxter R. #LB-6. Presented at: IDSA 49th Annual
Meeting; Oct. 20-23, 2011; Boston.