Method: Serotype-specific immune status of pediatric patients of invasive pneumococcal disease (IPD) has not been fully investigated. 27 pediatric patients with IPD were examined for the serotype-specific immunoglobulin G (IgG) levels using enzyme-linked immunosorbent assay (ELISA) or OPI using a multiplexed opsonization assay after the episode of infection between June 2009 and March 2011 in Japan.
Result: The mean age of IPD cases were 25.5 months and male sex was 66.7%. 3 (11.1%) were vaccinated with 23-valent pneumococcal polysaccharide vaccine, 8 (34.8%) were vaccinated with 7-valent pneumococcal conjugate vaccine (PCV7) and 16 (59.3%) were unvaccinated before the episode of IPD. Predominant serotypes causing IPD were serotype 6B (n=12, 44.4%), 19F (n=5,18.5%), 14 (n=4, 14.8%), and 19A (n=3, 11.1%). Of 27 cases, serotype-specific IgG and OPI for the causing serotype were determined in sera from 22 cases (81.5 %) and 20 cases (74.1 %), respectively. While the levels of serotype-specific ELISA IgG widely ranged from 0.19 to 6.53 ug/ml for 22 cases, 17 of 20 cases (85.0 %) of the OPI were below 8. Of 12 IPD cases attributable to 6B serotype, two vaccine failures and 4 breakthrough infections were found. In 7 of 9 cases caused by serotype 6B (77.8%), no response was found in OPK for the serotype 6B after at least one dose of PCV7.
Conclusion:Our present data suggest that the OPI is an accurate indicator of serotype-specific immunity rather than ELISA IgG for pediatric IPD, and a serious concern of the immunogenicity to serotype 6B after vaccination with PCV7 has been raised in children in Japan.
N. Ishiwada, None