Immunogenicity of PCV-7 Vaccine in VLBW Infants

Streptococcus pneumoniae causes an estimated 10-25% of all pneumonias in the United States, and is responsible for an estimated 40,000 deaths per year. Invasive pneumococcal disease has a peak incidence of 235/100,000 among children aged 6-11 months. Pneumococcal meningitis carries a higher risk of death (15%) or neurodevelopmental impairment (12-28%) than Hib or Neisseria meningitides. Premature infants are at a higher risk for invasive disease with Streptococcus pneumoniae. The heptavalent pneumococcal-CRM197 conjugate vaccine (PCV-7) effectively prevents invasive pneumococcal disease in full-term infants, but was been incompletely studied in premature infants. The American Academy of Pediatrics (AAP) recommends that "prematurely born infants, including infants of low birth weight, should be immunized at the usual chronological age in most cases", but cautions that "some studies suggest a reduced immune response in very low-birth-weight infants (\<1500 g)." This observational study assessed the effectiveness of the PCV-7 vaccine to generate a sufficient immune response in a safe manner when given to very low birth weight (VLBW) infants in routine pediatric practice. We hypothesized that among VLBW infants, the frequency of estimated minimum protective antibody titers to PCV-7 (\>=0.15 μg/mL) would decrease with decreasing birth weight. Infants 501-1500g birth weight and \<32 0/7 weeks gestational age were enrolled from nine NICHD Neonatal Research Network centers from 2004 to 2006. Enrollment was stratified by weight group to yield approximately 20 infants per 100g increments from 501-1500g birth weight whose primary PCV-7 series was initiated before 3 months and completed by 8 months after birth. The infants' primary providers gave PCV-7 vaccination at 2, 4, and 6 months after birth. Infants had a single 2-ml blood sample drawn 4-6 weeks following the third dose of PCV-7. Antibodies for each of the seven vaccine serotypes included in PCV-7 were measured by enzyme-linked immunosorbent assay. Children were followed until 18-22 months corrected age to assess survival, infection, and neurodevelopmental outcomes.