Children whose parents refused the pertussis vaccine were 23 times more likely to contract the disease than were children whose parents allowed them to receive the vaccine, a case-control study found.
Of 156 pediatric pertussis cases identified in a large health care database, 18 (12%) had not received the pertussis vaccine because of parental refusal. Of the 595 matched controls, only 3 (0.5%) had parents who refused to have them vaccinated, Jason M. Glanz, Ph.D., and his colleagues reported (Pediatrics 2009;123:1446–51).
The study was conducted in Colorado, a state with generally high rates of childhood immunization, wrote Dr. Glanz of the Kaiser Permanente Colorado Institute for Health Research, Denver. “Despite high pertussis immunization rates in Colorado, herd immunity did not prevent a high relative risk for pertussis in vaccine refusers,” he and his colleagues observed. “This is likely because of a combination of waning immunity to pertussis in adolescents and adults, ongoing endemic circulation, the highly contagious nature of the bacterium, and frequent asymptomatic infections.”
The study offers a sobering look at the results of the growing trend of vaccine refusal, Dr. Randy Bergen said in an interview. Dr. Bergen, chair of the pediatric infectious disease section at Kaiser Permanente of Northern California, Walnut Creek, said the antivaccine campaigns of several outspoken celebrities continue to influence parental decisions about their children's health care. “And not only are these unvaccinated children being put at risk of contracting an infectious disease, they are putting vaccinated children at risk as well.”
The study examined pertussis vaccination rates and disease prevalence in children aged 2 months to 18 years enrolled in the Kaiser Permanente of Colorado health plan between 1996 and 2007. Each case of pertussis was matched to four randomly selected controls.
Children were considered “vaccine refusers” if their medical charts documented a parental refusal of one or more pertussis immunizations for nonmedical reasons. The review identified 156 children who had a confirmed diagnosis of pertussis during the study period. Of these, 17 (11%) had parents who refused all the recommended pertussis immunizations; 1 additional child received only one of the five recommended doses. Six percent had to be hospitalized for the illness. The mean duration of cough at diagnosis was 12 days.
The cases (mean age, 9 years) were matched with 595 controls, none of whom contracted the disease. Only three of the control children (0.5%) had parents who refused one or more pertussis immunizations. Children who were not vaccinated were 23 times more likely to contract pertussis than were vaccinated children.
Because some of the children in the primary analysis were not Kaiser members during the entire first 20 months of their life, when they would have received all four primary vaccine doses, the investigators conducted a secondary analysis of 27,748 children who were continuously enrolled in the program from 2 to 20 months of age. This cohort included 31 children with confirmed pertussis infections, who were matched with 308 controls. Among the cases, 13% had parents who refused the vaccine; only 0.7% of controls had parents who refused.
“The study highlights the need for effective risk communication between parents and physicians about vaccines and the diseases they prevent,” Dr. Glanz and his colleagues wrote.
Dr. Bergen, who is also a practicing pediatrician, agreed, saying that many parents who express concerns about vaccine safety feel more confident after hearing the scientific evidence of their safety. A second group, however, is tougher to convince. “These parents are adamant in their mistaken impression that vaccines are dangerous, and they will not be dissuaded by any information about the severity of the infections vaccines prevent, or the lack of any evidence that vaccines cause autism or any other harm.”
“This study suggests that parents who don't vaccinate are putting the community at risk, as well as their own children,” Dr. Bergen suggested. “It's similar to the secondhand smoke argument. I understand that those parents are entitled to their choice, but why is that choice more important than another parent's choice to vaccinate? I may not have the right to make the decision for a parent, but as a parent, I do have the right to have some input about the environment my child is in.”
Dr. Glanz and his associates indicated that they had no conflicts to disclose. Dr. Bergen likewise had no conflicts of interest.