Efficacy of Pertussis Vaccines for Adolescents and Adults
Efficacy of Pertussis Vaccines for Adolescents and Adults
Objective. To assess the effectiveness of reduced acellular pertussis (Tdap) vaccines in adolescents and adults.
Setting. Kaiser Permanente Northern California.
Design. Case-control study.
Participants. All polymerase chain reaction (PCR) confirmed cases of pertussis in members aged 11 years and older from January 2006 to December 2011. We compared the Tdap vaccination status of PCR positive cases with two control groups: people testing negative for pertussis by PCR and closely matched people from the general Kaiser Permanente Northern California population.
Main Outcome Measure. PCR confirmed pertussis. The association of Tdap vaccination with the odds of pertussis infection was estimated by conditional logistic regression, with adjustment for calendar time, pertussis vaccine type received in early childhood, age, sex, race or ethnic group, and medical clinic. We calculated Tdap vaccine effectiveness as 1 minus the adjusted odds ratio.
Results. The study population included 668 PCR positive cases, 10 098 PCR negative controls, and 21,599 Kaiser Permanente Northern California matched controls. Tdap vaccination rates were 24.0% in PCR positive cases and 31.9% in PCR negative controls (P<0.001). The adjusted estimate of effectiveness of Tdap vaccination against pertussis was 53.0% (95% confidence interval 41.9% to 62.0%) in the comparison with PCR controls, and 64.0% (55.5% to 70.9%) in the comparison with Kaiser Permanente Northern California controls.
Conclusion. Tdap vaccination was moderately effective at preventing PCR confirmed pertussis among adolescents and adults.
Pertussis is a worldwide, cyclic illness, which was concentrated in children under 5 years of age during the pre-vaccine era. After widespread use of whole cell pertussis, tetanus, and diphtheria toxoid vaccines for infants starting in the United States in 1948, the incidence of pertussis decreased noticeably and infants under 6 months and adolescents became the most susceptible age groups. Though infants experience most of the mortality from pertussis, adolescents and adults serve as reservoirs and vectors of infection and comprise about half of all cases. During the 1990s, safety concerns regarding whole cell pertussis vaccines prompted the United States to switch to acellular pertussis vaccines. Despite high vaccine coverage in infants and children, since the 1980s the United States has experienced periodic outbreaks of pertussis, with incidence increasing over time. Reasons for the increase are likely varied, but studies of recent outbreaks have found that acellular pertussis vaccines for children are less effective than earlier whole cell formulations, and that protection wanes substantially after the last dose.
Tetanus toxoid, reduced diphtheria toxoid, and reduced acellular pertussis (Tdap) vaccines were developed to improve protection against pertussis among adolescents and adults. Two Tdap vaccines were licensed in 2005 on the basis of immunogenicity measures comparable to the acellular pertussis vaccines already approved for infants, despite uncertainty about the relation between these measures and effectiveness. That same year, the US Advisory Committee on Immunization Practices recommended a single dose of Tdap to replace the next scheduled tetanus diphtheria (Td) booster for all people aged 11-64, and in 2012 the committee extended its recommendation for routine Tdap vaccination to all people aged 65 and older.
Post-licensure studies of the Tdap vaccines showed high effectiveness, but the studies were limited by small numbers of pertussis cases and by use of populations who had all received whole cell pertussis vaccines as children. Studies to date provide little or no information as to the effectiveness of the Tdap booster when administered to the newly emerging cohort of adolescents previously vaccinated entirely with acellular pertussis instead of whole cell pertussis vaccines.
In 2010 the incidence of pertussis in California rose to its highest level in the past 50 years. With data from a six year period including this outbreak, we assessed the effectiveness of Tdap vaccination in reducing the risk of pertussis among adolescents and adults who had received whole cell pertussis vaccines as children as well as among younger adolescents who had only ever received acellular pertussis vaccines.
Abstract and Introduction
Abstract
Objective. To assess the effectiveness of reduced acellular pertussis (Tdap) vaccines in adolescents and adults.
Setting. Kaiser Permanente Northern California.
Design. Case-control study.
Participants. All polymerase chain reaction (PCR) confirmed cases of pertussis in members aged 11 years and older from January 2006 to December 2011. We compared the Tdap vaccination status of PCR positive cases with two control groups: people testing negative for pertussis by PCR and closely matched people from the general Kaiser Permanente Northern California population.
Main Outcome Measure. PCR confirmed pertussis. The association of Tdap vaccination with the odds of pertussis infection was estimated by conditional logistic regression, with adjustment for calendar time, pertussis vaccine type received in early childhood, age, sex, race or ethnic group, and medical clinic. We calculated Tdap vaccine effectiveness as 1 minus the adjusted odds ratio.
Results. The study population included 668 PCR positive cases, 10 098 PCR negative controls, and 21,599 Kaiser Permanente Northern California matched controls. Tdap vaccination rates were 24.0% in PCR positive cases and 31.9% in PCR negative controls (P<0.001). The adjusted estimate of effectiveness of Tdap vaccination against pertussis was 53.0% (95% confidence interval 41.9% to 62.0%) in the comparison with PCR controls, and 64.0% (55.5% to 70.9%) in the comparison with Kaiser Permanente Northern California controls.
Conclusion. Tdap vaccination was moderately effective at preventing PCR confirmed pertussis among adolescents and adults.
Introduction
Pertussis is a worldwide, cyclic illness, which was concentrated in children under 5 years of age during the pre-vaccine era. After widespread use of whole cell pertussis, tetanus, and diphtheria toxoid vaccines for infants starting in the United States in 1948, the incidence of pertussis decreased noticeably and infants under 6 months and adolescents became the most susceptible age groups. Though infants experience most of the mortality from pertussis, adolescents and adults serve as reservoirs and vectors of infection and comprise about half of all cases. During the 1990s, safety concerns regarding whole cell pertussis vaccines prompted the United States to switch to acellular pertussis vaccines. Despite high vaccine coverage in infants and children, since the 1980s the United States has experienced periodic outbreaks of pertussis, with incidence increasing over time. Reasons for the increase are likely varied, but studies of recent outbreaks have found that acellular pertussis vaccines for children are less effective than earlier whole cell formulations, and that protection wanes substantially after the last dose.
Tetanus toxoid, reduced diphtheria toxoid, and reduced acellular pertussis (Tdap) vaccines were developed to improve protection against pertussis among adolescents and adults. Two Tdap vaccines were licensed in 2005 on the basis of immunogenicity measures comparable to the acellular pertussis vaccines already approved for infants, despite uncertainty about the relation between these measures and effectiveness. That same year, the US Advisory Committee on Immunization Practices recommended a single dose of Tdap to replace the next scheduled tetanus diphtheria (Td) booster for all people aged 11-64, and in 2012 the committee extended its recommendation for routine Tdap vaccination to all people aged 65 and older.
Post-licensure studies of the Tdap vaccines showed high effectiveness, but the studies were limited by small numbers of pertussis cases and by use of populations who had all received whole cell pertussis vaccines as children. Studies to date provide little or no information as to the effectiveness of the Tdap booster when administered to the newly emerging cohort of adolescents previously vaccinated entirely with acellular pertussis instead of whole cell pertussis vaccines.
In 2010 the incidence of pertussis in California rose to its highest level in the past 50 years. With data from a six year period including this outbreak, we assessed the effectiveness of Tdap vaccination in reducing the risk of pertussis among adolescents and adults who had received whole cell pertussis vaccines as children as well as among younger adolescents who had only ever received acellular pertussis vaccines.
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