Although vaccines against Bordetella pertussis, the bacterium that causes pertussis (whooping cough) are widespread, it is still a prevalent disease, researchers from Kaiser Permanente Medical Center, San Rafael, CA, USA, reported in the journal Clinical Infectious Diseases. As background information, the authors explained that several experts had been wondering whether acellular vaccine might not be as long-lasting as had been previously thought.
Senior author, Dr. David Witt and team examined pertussis incidence during a large outbreak, as well as the efficacy of the vaccination in a community in Marin County; a well-vaccinated community. The medical center cares for 40% of the Marin Country population, approximately 135,000 people.
During a large whooping cough outbreak from March to October 2010, they identified 171 patients with a positive PCR (Polymerase Chain Reaction) test for B. pertussis. The authors gathered data on patients’ demographics as well as who had been vaccinated, and when.
171 cases of clinical whooping cough were identified, 132 of whom were children. The researchers noticed that there was an evident increase in pertussis cases among children aged 8 to 12 years.
Positive test results among children up to the age of six years were low, and rose as their age approached pre-adolescence, with a peak at 12 years. Rates of vaccinated children with PCR positive results were pretty much the same when vaccinated and unvaccinated groups were compared in the 8-12 year age group.
The researchers reported the following vaccination effectiveness according to age:
- 2-7 years – 41%
- 8-12 years – 24%
- 13-18 years – 79%
As shown above, vaccine effectiveness dropped considerably in the 8-12 year age-group.
In an Abstract in the same journal, the authors concluded:
“Our data suggests that the current schedule of acellular pertussis vaccine doses is insufficient to prevent outbreaks of pertussis. We noted a markedly increased rate of disease from age 8 through 12, proportionate to the interval since the last scheduled vaccine. Stable rates of testing ruled out selection bias. The possibility of earlier or more numerous booster doses of acellular pertussis vaccine either as part of routine immunization or for outbreak control should be entertained.”
Written by Christian Nordqvist