Despite the growing evidence of waning immunity of acellular pertussis vaccines, unvaccinated children are more likely to contract pertussis than partially vaccinated or vaccinated children of all ages, according to results published in Clinical Infectious Diseases of a statewide study of children living in Oregon.
Juventila Liko, MD, MPH, of the Oregon Immunization Program, and colleagues reviewed data from Oregon’s statewide reportable disease database. The study cohort consisted of patients with pertussis aged 2 months to 19 years with disease onset during 2012. Patients who received a pertussis vaccine less than 2 weeks before onset were excluded from the study.
Overall, 709 child cases of pertussis were reported in Oregon during 2012. Children aged 2 months to 6 years accounted for 289 cases of pertussis. Of these, 129 (45%) children were up to date for their age with diphtheria-tetanus toxoids-acellular pertussis vaccines, 71 (24%) were partially vaccinated and 89 (31%) were unvaccinated. Of those unvaccinated, 70% were unvaccinated because parents declined consent.
Children aged 7 to 10 years accounted for 153 cases, of whom 121 (79%) were fully vaccinated. Researchers found lower rates of tetanus-diphtheria-acellular pertussis vaccination among children younger than 11 years. Seventy-six percent of children aged 13 to 16 years received Tdap, likely due to Oregon’s school requirements, according to the study researchers.
Children who were unvaccinated for pertussis were more likely to develop the disease and had RRs ranging from 1.9 to 20.6. Those partially vaccinated had a 1.3- to threefold risk for pertussis. Vaccine effectiveness ranged from 47% among children aged 13 to 16 years to 95% among children aged 15 to 47 months.
“Our data demonstrate the effectiveness of pertussis vaccination among all age cohorts of children: No matter the age, an unvaccinated child was more likely to contract pertussis than a vaccinated or partially vaccinated child,” Liko and colleagues concluded.
Disclosure: The researchers report no relevant financial disclosures.