Immunoglobulin G antibody responses to polyvalent pneumococcal vaccine in children in the highlands of Papua New Guinea.

The immunoglobulin G (IgG) antibody responses to a pneumococcal polysaccharide vaccine were examined for 480 children aged 3 months to 5 years and living in Tari, Southern Highlands Province, Papua New Guinea. Antipneumococcal IgG to the seven serotypes most frequently causing invasive disease (types 2, 5, 6B, 7F, 14, 19F, and 23F) was measured by an enzyme-linked immunosorbent assay in serum collected before vaccination and 1 and 6 months after vaccination. Prevaccination antibody levels fell rapidly after 3 months of age and remained low throughout the first 2 years of life. One month after vaccination, geometric mean titers of antipneumococcal IgG to serotypes 2, 7F, 23F, and 5 were at least twice those of antibodies in nonvaccinated children of the same age from the ages of 5, 6, 9, and 12 months onwards, respectively; postvaccination antibody responses to serotypes 6B, 14, and 19F rose gradually during the second year of life. Elevated antibody titers to serotypes 2 and 7F were maintained 6 months after vaccination. Thus, young Papua New Guinean children are capable of mounting a good immune response to some pneumococcal capsular polysaccharides from a young age, and the antibody responses to capsular polysaccharides are consistent with studies in developed countries. However, in Papua New Guinea, the serogroup distribution of invasive disease matches the immunogenic components of the pneumococcal polysaccharide vaccine more closely than in developed countries, a fact which helps to explain the results of controlled trials in Papua New Guinea, in which this vaccine prevented death and severe morbidity from pneumonia in young children.