Abstract
BackgroundChina is approaching measles elimination, but indigenous measles still circulates. County L in China has reported measles-containing vaccine (MCV) coverage rates >95% since 2000. Despite high reported coverage, a large measles outbreak occurred among young children in L County. We measured MCV coverage using 5 different methods during an investigation on this outbreak and compared our estimates with reported rates.MethodsReported coverage rates are determined by aggregating clinic-based data across the county: doses administered in each clinic divided by the number of children registered in each clinic. Our methods estimated coverage for the 2010–2012 birth cohort, and were (1) administrative method: doses administered in clinics divided by the birth cohort recorded in the Statistical Year Book, (2) house-to-house convenience-sample survey of children living near cases, (3) vaccination clinic records review, (4) determination of a convenience sample of measles outbreak cases’ vaccination statuses and using the field vaccine efficacy outbreak equation to estimate population coverage, and (5) a seroprevalence survey using a convenience sample of residual blood samples from hospitals.ResultsThe measles outbreak totaled 215 cases, representing an incidence of 195.8 per million population. Our estimated MCV coverage rates were: (1) administrative method: 84.1%-87.0% for MCV1 and 80.3%-90.0% for MCV2, (2) in-house survey: 83.3% of 9–17 month children received MCV1, and 74.5% of 24–47 month children received MCV2, (3) clinic record review: 85.5% of 9–17 month children received MCV1, and 73.2% of 24–59 month children received MCV2, (4) field VE method: 83.6% of 9–47 month children received one or more MCV doses, and (5) serology: seropositive rates were <80% in the 12–17 and 18–23 month age cohorts.ConclusionsCompared with reported coverage >95%, our 5 coverage assessments all showed substantially lower coverage. China should evaluate guidelines for reporting vaccination coverage and identify feasible improvements to the assessment methods.
Highlights
China is approaching measles elimination, but indigenous measles still circulates
House-to-house coverage survey During the measles outbreak investigation, we identified a sample of children who had not acquired measles but who lived near a convenience sample of the measles cases
Coverage estimation From 2010 through 2012, the annual number of doses of MCV1 delivered through routine immunization in L County ranged between 13,718 and 14,452 doses, and the annual number of MCV2 doses ranged between 13,874 and 14,711 doses
Summary
China is approaching measles elimination, but indigenous measles still circulates. County L in China has reported measles-containing vaccine (MCV) coverage rates >95% since 2000. The World Health Organization Western Pacific Region has been striving to eliminate measles since 2005 [1] and set a goal to eliminate measles in the region by 2012 China adopted this goal and endorsed an action plan for measles elimination in 2006 that included continuing a two-dose measles-containing vaccine (MCV) strategy (administered at 8 months and 18–23 months of age), and called for routine measles vaccine coverage to be greater than 95% for both doses in every county, while using supplementary immunization activities (SIAs) to close immunity gaps among children [2]. Between January and October 2013, there were over 26,000 measles cases reported in China, which was 1.7 times more than case number of the same time period in 2011 and 4.6 times more than that in 2012 Of these cases, 68% were among children under 5 years of age [3], raising the concern that timely, 2-dose MCV coverage may not be high enough to eliminate measles outbreaks among young children
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