Effectiveness of abbreviated and delayed 7-valent pneumococcal conjugate vaccine dosing regimens

We estimated the effectiveness of abbreviated regimens of 7-valent pneumococcal conjugate vaccine (PCV7) based on serotyped cases of invasive pneumococcal disease (IPD) in children under 5 reported from 2001 to 2004 to two US surveillance programs. Vaccination regimens included in the analysis were 1 dose < 3 months old, 2 doses < 5 months old, 3 doses < 7 months old, full schedule (3 doses and a booster), 1 dose at 12-23 months, and 2 doses at 12-23 months. Vaccine effectiveness (VE) was calculated as (1 - Mantel-Haenszel summary odds ratio in vaccinated children, as compared to unvaccinated children) × 100% for each regimen, stratifying by year. Among 400 eligible cases, for vaccine-type IPD, VE was 90.5% for the full schedule, 76.6% for 3 doses < 7 months old, and 70.5% for 2 doses < 5 months old; 1 dose < 3 months provided no significant protection. No regimen provided significant protection against vaccine-related serotypes. Data for regimens begun at 12-23 months were inconclusive. These data support the use of the 2-dose and 3-dose infant PCV7 regimens when the full series cannot be delivered and detail the limitations of abbreviated dosing regimens.