Waning population immunity to measles in Taiwan.

To evaluate the population immunity to measles in Taiwan where the coverage rate of the measles vaccine was >95% for more than a decade, anti-measles IgG was determined in 3552 Taiwanese volunteers in 2007. The overall seroprevalence was 74.7% (95% confidence interval [CI]: 73.3-76.1%). In subgroups aged 2-25 years, to whom at least 2 doses of measles-containing vaccine were given, there was a declining trend of seropositivity with age from 94.5% at 2 years to 50.6% at 21-25 years (p<0.0001). Age (odds ratio [OR]: 1.0464, 95% CI: 1.043-1.085) and male gender (OR: 1.466, 95% CI: 1.131-1.901) were independent factors predicting seronegative sera in this population. Seroprevalence was uniformly >95% in the older population (≥ 35 years) who had not been immunized against measles. The waning vaccine-induced immunity may have impact on the control of measles in the future, especially when the vaccinated population becomes older.