Measles IgG seroprevalence prior to mass vaccination in Taiwan

Measles vaccine was licensed for use in Taiwan in 1968 and mass vaccination has been implemented since 1978. Serological surveys were conducted to characterize measles seroepidemiology prior to mass vaccination.

Measles IgG was quantitatively measured in 1564 serum samples collected from four populations (nationwide, urban, rural, and mountain areas) during 1974-80 with a commercial EIA kit. The nationwide samples covered age groups from 3 months to 19 years, but the other three samples only covered school-aged children. The cut-off value of seropositivity was set at 100 mIU/ml.

In the nationwide samples, measles IgG seroprevalence decreased from 50% at 3-5 months to 13% at 6-11 months, then increased rapidly to 55% at 1-1.9 years and reached 98% at 7-7.9 years of age; this was maintained to young adulthood. In all four samples, seroprevalence also reached >97% in individuals >10 years of age. Semiquantitative analysis found that 24%(10/42) of 1-1.9-year-old children but only 4%(1/24) of 15-19-year-old adolescents had low level measles IgG (100-399 mIU/ml). In addition, the distribution of measles IgG level in 1-1.9-year-old children had two peaks at 200-399 and 1600-3199 mIU/ml, whereas only one peak at 1600-3199 mIU/ml had been found in 15-19-year-old adolescents. The median age of measles infection (i.e. 50% seroprevalence) in Taiwan was 1.4 and 2.1 years, respectively, before and after excluding individuals with measles IgG 100-399 mIU/ml that may have resulted from vaccination.

Measles seroepidemiology in Taiwan in the 1970s seemed to be more similar to that in a developing country rather than in an industrialized country, and there was a low median age of infection.