Case-Control Study of Vaccination History in Relation to Pertussis Risk
Case-Control Study of Vaccination History in Relation to Pertussis Risk
Background: Between September and December 2003, an outbreak of pertussis occurred in Cass County, MO, mostly among adolescent school children.
Methods: We conducted a 1:2 matched case-control study among school children and used conditional logistic regression to evaluate risk factors for pertussis, including the total number of vaccine doses received, age at administration of each dose of vaccine and the type of vaccine (whole cell or acellular).
Results: Of all 127 pertussis cases reported in this outbreak, the majority were adolescents (10-19 years of age, 50%) and adults (20 years or older, 22%); only 10% were infants and children less than 5 years of age. Because the focus of our investigation was on school-aged children, we enrolled 237 students (79 cases and 158 controls) in our study. Students missing at least one dose of the vaccine had higher risk for pertussis than those who received all 5 doses (odds ratio [OR], 2.36; 95% confidence interval [CI], 1.17-4.77). Early administration of the fifth dose of the vaccine at age 4 years was significantly associated with risk for pertussis compared with vaccination at age 5 years (adjusted OR, 2.45; 95% CI, 1.16-5.16). A short time interval (<36 months) between the fourth and fifth doses of the vaccine also tended to increase the risk for pertussis, although this association was not statistically significant. The type of vaccine was not a significant risk factor.
Conclusion: Administering all 5 doses of pertussis vaccine and the fifth dose at age 5 years with at least 36 months between the fourth and fifth doses provided the best protection against pertussis among children and adolescents in this outbreak.
Pertussis continues to be a significant cause of morbidity among U.S. children. There has been a resurgence of pertussis in older children, adolescents and adults since the early 1980s. Waning vaccine immunity permits the disease to affect adolescents and adults who in turn transmit the disease to unimmunized or incompletely immunized infants and children. It is currently recommended that U.S. children receive a primary 3-dose series of pertussis vaccine at 2, 4 and 6 months of age followed by the fourth dose at age 15 to 18 months and the fifth dose at age 4 to 6 years.
Two recent studies using data from the National Immunization Survey reported that U.S. children rarely receive all vaccinations as recommended, and 74% of U.S. children were delayed for one or more vaccinations during the first 24 months of life. Delayed pertussis immunizations may increase the risk for developing pertussis later in life, but currently available evidence has been inconsistent and inconclusive. Little is known whether early administration of the fifth dose affects pertussis risk.
Between September and December 2003, an outbreak of pertussis, mostly among school children, occurred in Cass County, MO. As part of the outbreak investigation and control effort, a case-control study was conducted to evaluate various aspects of pertussis vaccination in relation to the risk of pertussis. These aspects included the total number of vaccine doses received, age at administration of each dose of the vaccine, type of vaccine received (whole cell or acellular) and whether the vaccine was administered by a private healthcare provider or at a public health clinic.
Abstract and Introduction
Abstract
Background: Between September and December 2003, an outbreak of pertussis occurred in Cass County, MO, mostly among adolescent school children.
Methods: We conducted a 1:2 matched case-control study among school children and used conditional logistic regression to evaluate risk factors for pertussis, including the total number of vaccine doses received, age at administration of each dose of vaccine and the type of vaccine (whole cell or acellular).
Results: Of all 127 pertussis cases reported in this outbreak, the majority were adolescents (10-19 years of age, 50%) and adults (20 years or older, 22%); only 10% were infants and children less than 5 years of age. Because the focus of our investigation was on school-aged children, we enrolled 237 students (79 cases and 158 controls) in our study. Students missing at least one dose of the vaccine had higher risk for pertussis than those who received all 5 doses (odds ratio [OR], 2.36; 95% confidence interval [CI], 1.17-4.77). Early administration of the fifth dose of the vaccine at age 4 years was significantly associated with risk for pertussis compared with vaccination at age 5 years (adjusted OR, 2.45; 95% CI, 1.16-5.16). A short time interval (<36 months) between the fourth and fifth doses of the vaccine also tended to increase the risk for pertussis, although this association was not statistically significant. The type of vaccine was not a significant risk factor.
Conclusion: Administering all 5 doses of pertussis vaccine and the fifth dose at age 5 years with at least 36 months between the fourth and fifth doses provided the best protection against pertussis among children and adolescents in this outbreak.
Introduction
Pertussis continues to be a significant cause of morbidity among U.S. children. There has been a resurgence of pertussis in older children, adolescents and adults since the early 1980s. Waning vaccine immunity permits the disease to affect adolescents and adults who in turn transmit the disease to unimmunized or incompletely immunized infants and children. It is currently recommended that U.S. children receive a primary 3-dose series of pertussis vaccine at 2, 4 and 6 months of age followed by the fourth dose at age 15 to 18 months and the fifth dose at age 4 to 6 years.
Two recent studies using data from the National Immunization Survey reported that U.S. children rarely receive all vaccinations as recommended, and 74% of U.S. children were delayed for one or more vaccinations during the first 24 months of life. Delayed pertussis immunizations may increase the risk for developing pertussis later in life, but currently available evidence has been inconsistent and inconclusive. Little is known whether early administration of the fifth dose affects pertussis risk.
Between September and December 2003, an outbreak of pertussis, mostly among school children, occurred in Cass County, MO. As part of the outbreak investigation and control effort, a case-control study was conducted to evaluate various aspects of pertussis vaccination in relation to the risk of pertussis. These aspects included the total number of vaccine doses received, age at administration of each dose of the vaccine, type of vaccine received (whole cell or acellular) and whether the vaccine was administered by a private healthcare provider or at a public health clinic.
