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Waning Tdap Effectiveness in Adolescents
Pediatrics
February 2016
Nicola P. Klein, Joan Bartlett, Bruce Fireman, Roger Baxter
Waning Tdap Effectiveness in Adolescents
Pediatrics
February 2016
Nicola P. Klein, Joan Bartlett, Bruce Fireman, Roger Baxter
Abstract
BACKGROUND AND OBJECTIVE: Because the effectiveness of diphtheria-tetanus-acellular pertussis (DTaP) vaccine wanes substantially after the fifth dose at ages 4 to 6 years, there is a growing cohort of adolescents who rely on tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) for protection against pertussis. Yet despite high Tdap vaccine coverage among adolescents, California experienced large pertussis outbreaks in 2010 and 2014. We investigated Tdap vaccine effectiveness (VE) and waning within Kaiser Permanente Northern California among adolescents exclusively vaccinated with DTaP vaccines.
METHODS: We modeled pertussis risk in relation to Tdap vaccination status among adolescents beginning on their 10th birthday. We estimated the hazard ratio (HR) for each subsequent year after Tdap compared with unvaccinated adolescents by using Cox regression, adjusting for calendar time, age, gender, race, and facility. We calculated VE as 1 − HR. We also treated time since Tdap vaccination as a continuous variable and estimated the change in the HR per 1-year increase since vaccination.
RESULTS: On the basis of 1207 pertussis cases, Tdap VE during the first year after vaccination was 68.8% (95% confidence interval [CI] 59.7% to 75.9%), decreasing to 8.9% (95% CI –30.6% to 36.4%) by ≥4 years after vaccination. Adolescents who were more remote from Tdap were significantly more likely to test positive for pertussis than were those vaccinated more recently (HR per year 1.35, 95% CI 1.22 to 1.50).
CONCLUSIONS: Routine Tdap did not prevent pertussis outbreaks. Among adolescents who have only received DTaP vaccines in childhood, Tdap provided moderate protection against pertussis during the first year and then waned rapidly so that little protection remained 2-3 years after vaccination..
Abbreviations:
CI — confidence interval
DTaP — diphtheria-tetanus-acellular pertussis
ED — emergency department
KPNC — Kaiser Permanente Northern California
HR — hazard ratio
PCR — polymerase chain reaction
P-Y — person-years
Tdap — tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis, adsorbed
VE — vaccine effectiveness
What’s Known on This Subject:
Diphtheria, tetanus toxoids, acellular pertussis (DTaP) vaccine effectiveness wanes after the fifth dose, and adolescents who have only received DTaP vaccines rely on reduced antigen content acellular pertussis (Tdap) vaccinefor protection against pertussis. Despite high Tdap vaccine coverage among adolescents, California experienced large pertussis outbreaks in 2010 and 2014.
What This Study Adds:
Routine Tdap vaccination did not prevent pertussis outbreaks in adolescents. Among adolescents previously vaccinated only with DTaP, Tdap provided moderate protection during the first year and then waned rapidly so that little protection remained 2-3 years after vaccination.
BACKGROUND AND OBJECTIVE: Because the effectiveness of diphtheria-tetanus-acellular pertussis (DTaP) vaccine wanes substantially after the fifth dose at ages 4 to 6 years, there is a growing cohort of adolescents who rely on tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) for protection against pertussis. Yet despite high Tdap vaccine coverage among adolescents, California experienced large pertussis outbreaks in 2010 and 2014. We investigated Tdap vaccine effectiveness (VE) and waning within Kaiser Permanente Northern California among adolescents exclusively vaccinated with DTaP vaccines.
METHODS: We modeled pertussis risk in relation to Tdap vaccination status among adolescents beginning on their 10th birthday. We estimated the hazard ratio (HR) for each subsequent year after Tdap compared with unvaccinated adolescents by using Cox regression, adjusting for calendar time, age, gender, race, and facility. We calculated VE as 1 − HR. We also treated time since Tdap vaccination as a continuous variable and estimated the change in the HR per 1-year increase since vaccination.
RESULTS: On the basis of 1207 pertussis cases, Tdap VE during the first year after vaccination was 68.8% (95% confidence interval [CI] 59.7% to 75.9%), decreasing to 8.9% (95% CI –30.6% to 36.4%) by ≥4 years after vaccination. Adolescents who were more remote from Tdap were significantly more likely to test positive for pertussis than were those vaccinated more recently (HR per year 1.35, 95% CI 1.22 to 1.50).
CONCLUSIONS: Routine Tdap did not prevent pertussis outbreaks. Among adolescents who have only received DTaP vaccines in childhood, Tdap provided moderate protection against pertussis during the first year and then waned rapidly so that little protection remained 2-3 years after vaccination..
Abbreviations:
CI — confidence interval
DTaP — diphtheria-tetanus-acellular pertussis
ED — emergency department
KPNC — Kaiser Permanente Northern California
HR — hazard ratio
PCR — polymerase chain reaction
P-Y — person-years
Tdap — tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis, adsorbed
VE — vaccine effectiveness
What’s Known on This Subject:
Diphtheria, tetanus toxoids, acellular pertussis (DTaP) vaccine effectiveness wanes after the fifth dose, and adolescents who have only received DTaP vaccines rely on reduced antigen content acellular pertussis (Tdap) vaccinefor protection against pertussis. Despite high Tdap vaccine coverage among adolescents, California experienced large pertussis outbreaks in 2010 and 2014.
What This Study Adds:
Routine Tdap vaccination did not prevent pertussis outbreaks in adolescents. Among adolescents previously vaccinated only with DTaP, Tdap provided moderate protection during the first year and then waned rapidly so that little protection remained 2-3 years after vaccination.