7-Valent pneumococcal conjugate vaccine and lower respiratory tract infections: Effectiveness of a 2-dose versus 3-dose primary series

Background: Immunogenicity studies suggest antibody responses from a 7-valent pneumococcal conjugate vaccine (PCV7) regimen consisting of 2 doses in the primary series are less immunogenic, for at least several vaccine serotypes, compared with a regimen consisting of 3 doses; evidence of effectiveness for prevention of invasive pneumococcal disease for both regimens is available but comparative data are lacking for prevention of lower respiratory tract diseases (LRTD). Methods: We compared rates of LRTD between children who were born in 2002 and received 2 versus 3 PCV7 doses in the primary series, both before and after receipt of the booster dose, using a retrospective matched-cohort design and health insurance claims data. Two-dose and 3-dose children were matched (1:1) using propensity scoring. Cumulative rates of hospital admissions and outpatient visits for LRTD were tallied during the post-primary/pre-booster period and the post-booster period (to age 3 years), respectively. Results: During the post-primary/pre-booster period, 3-dose children (n=3293) had 7.8 (95% CI: 0.8 to 14.8) fewer LRTD-related hospital admissions (per 1000 children) and 57 (95% CI: -6 to 128) fewer LRTD-related outpatient visits (per 1000 children) than matched 2-dose subjects (n=3293). During the post-booster period, the numbers of LRTD-related hospital admissions and outpatient visits did not differ significantly between 3-dose and 2-dose children. Conclusions: Our findings suggest that a 2-dose PCV7 primary series, while conferring savings from reduced vaccine costs in comparison with a 3-dose primary series, also may confer less protection against LRTD in the first year of life, at least during the period soon after the vaccine is introduced. (C) 2009 Published by Elsevier Ltd.