Serum bactericidal activity and isotype distribution of antibodies in toddlers and schoolchildren after vaccination with RIVM hexavalent PorA vesiclevaccine

A clinical phase II trial with the RIVM hexavalent OMV vaccine containing s ix different PorAs was carried out in toddlers (2-3 years) and schoolchildr en (7-8 years) in The Netherlands. Children were vaccinated three times (0, 2, 8 months). Sera after two and three vaccinations were analysed for seru m bactericidal activity (SBA) and isotype distribution in whole cell enzyme linked immunosorbent assay (ELISA). The SBA after vaccination against the six PorAs was significantly different. We investigated whether the age spec ific and PorA specific differences in SBA titers correlated with difference s in PorA specific IgG isotype distribution. The SBA titers were higher in toddlers compared with schoolchildren. After vaccination, IgG I antibodies dominated the response followed by IgG3 antibodies. IgG2 levels were low. w hereas IgG4 was not detected. Irrespective of PorA, IgG total and isotype s pecific titers after two and three vaccinations were significantly higher i n toddlers than in schoolchildren. A weak correlation was found between IgG total or IgG I and SBA. Although the immunogenicity of the six PorAs is ve ry different, the isotype distribution was similar for all six tested PorAs . We conclude that the RIVM hexavalent PorA vesicle vaccine induces bacterici dal antibodies mainly of the IgG1 and IgG3 isotypes that are considered to be most important for protection against disease. The isotype distribution of the response is not age-dependent. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.