Long-term antibody persistence study (3 years after last dose) of the 7-valent pneumococcal conjugate vaccine in young children in China

In a previous study, Chinese infants were vaccinated with 7-valent pneumococcal conjugate vaccine (PCV7) ⩾7 days before routine diphtheria, tetanus, and acellular pertussis vaccine (DTaP); PCV7 administered concomitantly with DTaP (PCV7 + DTaP); or DTaP alone. This study examined antibody persistence at a single time point 3 years after the last vaccination. Children who participated in the prior PCV7 study were eligible to participate. A single blood sample was drawn at enrollment. Immunoglobulin G (IgG) geometric mean concentrations (GMCs) specific to the PCV7 serotypes and percentages of subjects with IgG ⩾0.35 μg/mL were compared for subjects receiving PCV7 versus PCV7 + DTaP (concomitant) and for PCV7 or PCV7 + DTaP (concomitant) versus DTaP alone. IgG concentrations at 3 years after the last vaccination were also compared with those after the infant series and toddler dose. Three years after the last vaccination with PCV7 or PCV7 + DTaP (concomitant), IgG GMCs for most PCV7 serotypes were lower than after the infant series or toddler dose but remained above prevaccination concentrations. IgG GMC were similar between the PCV7 and PCV7 + DTaP (concomitant) groups for 5 out of 7 serotypes but serotypes 4 and 19F were significantly lower in the PCV7 + DTaP (concomitant) recipients. Three years after the last vaccination, IgG GMCs were significantly higher for 6 of 7 PCV7 serotypes among those receiving PCV7 or PCV7 + DTaP (concomitant) compared with recipients of DTaP alone. Among subjects receiving DTaP alone, serotype-specific antibody concentrations were significantly higher for all serotypes 3 years after the last vaccination compared with after the infant series. Three years after PCV7 vaccination, serotype-specific antibodies were lower than after the primary infant series but higher than prevaccination levels and higher among subjects who received PCV7 compared with those who did not. The immune response was comparable in children who received PCV7 with and without concomitant DTaP. Clinical Trial Registration: NCT01298544