Waning immunity to measles in young adults and booster effects of revaccination in secondary school students.

The increasing proportions of adult cases were observed in the recent measles outbreaks in Zhejiang Province, China. In order to identify the high-risk age groups of measles for targeted intervention, a seroprevalence survey of measles antibody was conducted among 1961 participants aged 0-60 years randomly selected by age-stratified purpose sampling, and the effect of revaccination program in secondary school was evaluated in Zhejiang Province. The adjusted overall seropositivity rate of measles was 88% (95% confidence interval [CI]: 86-89%) with geometric mean titers (GMT), 976±86 mIU/ml. The seropositivity rate of measles was significantly lower in subjects aged 15-19 years than aged 5-9 years (90% vs 96%, χ(2)=5.21, p=0.022). Both seropositivity rate and GMT level of measles were higher in participants aged 10-14 years with ≥2 doses MCV than those with only 1 dose (95% vs 81%, 1276 mIU/ml vs 666 mIU/ml). The seropositivity rate increased from 91% to 100% after revaccination with MCV among 184 secondary school students. The proportions of measles cases aged ≥15 years were reduced gradually (χ(2)=55.47, p=0.000) from 2009 to 2011 after implementing the revaccination campaign on secondary school students since 2008. Our findings strongly suggested that a revaccination opportunity with MCV for adolescents helps to improve the population immunity, and it can be conducted effectively and practically in secondary school students.