Vaccinated children and adolescents with pertussis infections experience reduced illness severity and duration, Oregon, 2010-2012.

BACKGROUND: Bordetella pertussis causes severe respiratory illness among infants and adolescents. High proportions of breakthrough infection have been observed. To understand the effect of vaccination in the era of acellular pertussis vaccines (DTaP and Tdap), we assessed if vaccination status is associated with disease severity and duration.
METHODS: The Multnomah County Health Department conducts enhanced pertussis surveillance for 1.7 million residents in the Portland, Oregon, metropolitan area. Surveillance activities include ascertaining demographics, clinical presentation, cough duration, vaccination history, and other health outcomes. Utilizing Advisory Committee on Immunization Practices (ACIP) routine vaccination recommendations, we analyzed a cohort of persons aged 6 weeks to 18 years with confirmed pertussis to assess illness severity and duration by vaccination status. Analysis was conducted using both logistic regression (disease severity) and survival analysis (cough duration).
RESULTS: During 2010-2012, 98.7% (n = 624) of patients with confirmed pertussis in our cohort had vaccination, treatment, demographic, and outcome information. Among these patients, 45% (n = 286) were ACIP up to date with vaccinations. Ever-vaccinated cases were significantly less likely to be hospitalized or develop severe illness (adjusted odds ratio [aOR], 0.2; 95% confidence interval [CI], .1-.8 and aOR, 0.4; 95% CI, .2-.9, respectively). ACIP up-to-date patients stopped coughing significantly more rapidly than unvaccinated patients (adjusted hazard ratio, 1.7; 95% CI, 1.3-2.2).
CONCLUSIONS: Patients with pertussis vaccination had decreased morbidity characterized by less severe illness and significantly reduced illness duration. Therefore, vaccination is recommended among at-risk individuals, and research into the nature of the residual vaccine immunity is warranted.