Background: Heptavalent pneumococcal conjugate vaccine was licensed in the United States in February 2000 and, following national guidelines, universally distributed in Massachusetts starting in July 2000 to children younger than 2 years of age and selected children 2-5 years of age. We performed statewide surveillance for all cases of invasive pneumococcal disease (IPD) in children younger than 18 years of age to determine risk features and contribution of vaccine failure to ongoing pneumococcal invasive disease.
Methods: Massachusetts pediatric IPD cases were identified via enhanced passive surveillance of microbiology laboratory reports of pneumococcal isolates from sterile body sites of children younger than 18 years for 2 years starting in October 2001. Serotyping was performed on isolates of Streptococcus pneumoniae from normally sterile body fluid. Case demographic and clinical data (including dates of prior doses of PCV7) were collected via follow-up telephone interviews with case primary care providers and/or parents.
Results: Between October 1, 2001 and September 30, 2003, 191 cases of IPD were identified statewide (138 in children younger than 5 years). Annual incidence rate for IPD was 17.4 per 100,000 children younger than 5 years, representing a decline of 69% when compared with annual incidence rate of 56.9 per 100,000 from Massachusetts statewide active surveillance performed 1990-1991. In 2001-2003, 30% of cases occurred in the first year of life (36.5 per 100,000), representing a 7.8-fold increased risk compared with children older than 1 year of age. Race-specific annual incidence rates in blacks and Hispanics were 2.3-fold (95% confidence interval, 1.21-4.42) and 1.9-fold (95% confidence interval, 1.06-3.37), greater than in whites. Fifty-nine cases were reported to have underlying comorbid conditions. Serotyping was available for 136 of 191 (71%) cases younger than 18 years; of isolates available for serotyping, 40 (29%) were vaccine serotype (ST), 31 (23%) vaccine-related ST and 65 (48%) nonvaccine ST. Seven of 40 cases with IPD caused by vaccine ST received at least 3 doses of PCV7 vaccine before IPD.
Conclusions: Universal administration of PCV7 to children younger than 2 years of age and selective administration to children 2-5 years of age has resulted in a significant decline in IPD in Massachusetts. Children younger than 1 year of age, African American and Hispanic children and those with recognized comorbid illnesses (malignancy, human immunodeficiency virus, immune deficiency, nephrotic syndrome, etc.) continue to remain at risk for IPD. These risk features should be considered when evaluating febrile infants and children.