Durability of protection after 5 doses of acellular pertussis vaccine among 5-9 year old children in King County, Washington

Abstract

Purpose: Waning of immunity after vaccination with the acellular Pertussis (aP) vaccine has been proposed as one of the main reasons for pertussis resurgence in the US. In this study, we estimated time-varying vaccine effectiveness after 5 doses of aP vaccine.

Methods: We conducted a retrospective cohort study among children 5-9 years old (born between 2008 and 2012) living in King County, Washington, USA, who participated in the Washington State Immunization Information System. We estimated time-varying vaccine effectiveness after 5 doses of aP using smoothed scaled Schoenfeld residuals obtained from fitting Cox proportional hazards models to the data as well as piecewise constant Poisson regression.

Results: There were 55 pertussis cases in this cohort, of whom 22 (40%) were fully-vaccinated and 33 (60%) were under-vaccinated. Vaccine effectiveness (VE) remained high for up to 42 months after the fifth dose (VE(t) = 89%; 95% CI: 64%, 97%) as estimated using survival analysis methods and up to 4 years (VE(t) = 93%; 95% CI: 67%, 98%) as estimated using Poisson regression.

Conclusion: We did not find evidence for waning of vaccine effectiveness for up to four years after 5 doses of aP among 5 -9 years old children in King County, WA.

Keywords: Acellular pertussis vaccines; Pertussis resurgence; Schoenfeld residuals; Time-varying vaccine effectiveness; Vaccine effectiveness; Vaccine waning effects.