763. DTaP Effectiveness: Results from the California Pertussis Vaccine Effectiveness Assessment
Session: Oral Abstract Session: Pertussis Vaccines and Challenges
Friday, October 21, 2011: 2:45 PM
Room: 156ABC
Background: In 2010, California experienced its largest pertussis outbreak in over 60 years. A substantial burden of disease was in the 7-10 year-old age group, despite high vaccine coverage with the 5-dose pertussis vaccine series (DTaP). The age distribution of cases suggested protection from the series may wane following the 5th DTaP dose and prior to the adolescent booster dose (Tdap) recommended at 11 or 12 years of age.

Methods: We evaluated overall vaccine effectiveness (VE) and duration of protection following the DTaP series using an unmatched case-control design. Cases were children aged 4-10 years with pertussis reported in 15 counties from January through November 2010; controls were children in the same age group who received care from the providers reporting the cases. Vaccination histories were obtained from provider records and the California Immunization Registry. We used logistic regression to calculate odds ratios and estimate VE, accounting for clustering by county and provider. Waning of immunity was evaluated by assessing VE among specific age groups; further analyses will account for time since vaccination with the 5th DTaP dose.

Results: A total of 965 cases and 2,848 controls were included in this assessment; data collection for an additional 100 cases and 400 controls is ongoing. Based on interim analyses, the VE estimate across all ages for 5 DTaP doses compared to 0 doses was 85.9% (95% confidence interval (CI): 75.6 - 91.9). The recommended childhood vaccination schedule for pertussis permits a 4 dose schedule if the 4th dose is received after the 4th birthday. The preliminary VE estimate across all ages for the 4 dose schedule compared to 0 doses was 80.4% (95% CI: 62.5 - 89.8). The preliminary VE estimate for 5 doses compared to 0 doses decreased from 94.7% in the 4-5 year-olds to 84.9% in the 6-7 year-olds, and to 81.1% in the 8-10 year-olds.

Conclusion: Short term VE estimates for the DTaP series are consistent with pre-licensure estimates, offering additional evidence that the vaccine is working well. Although overall VE is good, the relative drop of 14% from the 4-5 year-olds to the 8-10 year-olds suggests that waning of immunity is occurring.

Subject Category: I. Adult and Pediatric Vaccines

Lara K. Misegades, PhD, MS1, Kathleen Winter, MPH2, Kathleen Harriman, PhD, MPH, RN2, John Talarico, DO, MPH2, Thomas Clark, MD, MPH1 and Stacey W. Martin, MS1, (1)Centers for Disease Control and Prevention, Atlanta, GA, (2)Immunization Branch, California Department of Public Health, Richmond, CA


L. K. Misegades, None

K. Winter, None

K. Harriman, None

J. Talarico, None

T. Clark, None

S. W. Martin, None

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.