Incidence of IPD with immunization. Crude incidences with 95% Poisson confidence intervals are shown for PPV-23 serotypes. The incidence of IPD within three years of immunization was significantly lower than the incidence before immunization (P < 0.001). A composite incidence >3 years post-immunization incidence (not shown; mean: 262, 95% CI: 131-469) was also significantly lower than incidence before immunization (P < 0.01).
Siemieniuk et al. BMC Infectious Diseases 2011 11:314 doi:10.1186/1471-2334-11-314