Methods: We conducted two matched case-control evaluations in Vermont to assess VE and duration of protection of the 5-dose childhood series (DTaP) and the adolescent dose (Tdap). The study population included children aged 4-10 years (DTaP evaluation) and adolescents aged 11-19 years (Tdap evaluation). All confirmed and probable pertussis cases reported to the Vermont Department of Health from 2011 to 2013 were included. Three controls were matched to each case based on healthcare provider alone (DTaP evaluation), or healthcare provider and birth year (Tdap evaluation). Vaccination history was obtained through provider records and parent interviews. Odds ratios (OR) comparing vaccine receipt between cases and controls were calculated using conditional logistic regression. VE was estimated as (1 - OR) × 100%. VE against Prn-deficient pertussis was estimated by restricting the study population to confirmed Prn-deficient cases and associated controls.
Results: The overall VE estimate for the 5-dose DTaP series was 84% (95% confidence interval [CI]: 58-94%). VE within 12 months of the fifth dose was 90% (95% CI: 71-97%), declining to 68% (95% CI: 10-88%) by 5-7 years post-vaccination. For the Tdap evaluation, overall VE was estimated at 70% (95% CI: 54-81%). VE within 12 months of Tdap vaccination was 76% (95% CI: 60-85%), declining to 56% (95% CI: 16-77%) at 2-4 years post-vaccination. Only Tdap VE could be estimated against Prn-deficient pertussis; it was not significantly different from the overall Tdap VE estimate.
Conclusion: Our DTaP and Tdap VE estimates are consistent with previous findings. This evaluation suggests Prn-deficiency does not impact Tdap VE against reported pertussis disease.
C. Finley, None
B. Goode, None
S. Schoenfeld, None
L. K. Misegades, None
S. W. Martin, None
A. M. Acosta, None