Figure. Incidence rate ratios (IRRs) of cases of gonorrhea by age group and birth cohort, adjusted for year of diagnosis in A) women and B) men, Norway. IRRs were calculated by using Poisson log-linear regression and adjusted for year of diagnosis. IRRs indicate incidence of gonorrhea in the vaccinated cohort (VC), (i.e., persons born during 1973–1976, 63% of whom were vaccinated), represented by triangles, and in the post-VC (i.e., those born after 1976), represented by circles, relative to the reference birth cohort, the pre-VC (i.e., persons born during 1965–1972), represented by the horizontal dotted line. Also shown are 95%s CI. Differences in the IRR were considered statistically significant if the CI did not include 1. A) Among women, the adjusted IRR in the VC 20–24 years was of borderline significance: 0.72, 95% CI 0.51–1.02. No effect was seen in other age groups or birth cohorts. B) Among men, a reduced adjusted incidence was evident for those 20–24 years of age in the VC (IRR 0.68, 95% CI 0.51–0.93) and persisted among post-VC who were 20–24 years of age (IRR 0.51, 95% CI 0.33–0.78). IRR increased for men 25–29 years of age in the post-VC (IRR 1.6, 95% CI 1.06-2.43).