Measles Outbreak at Religious Study Camp: Findings from Response Against Non-Vaccinated Population, Mie prefecture, Japan, 2019

  • Vaccine preventable diseases
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In 2015, the World Health Organization verified Japan for measles elimination . Nevertheless, tourist and business travelers have continued to occasionally import measles virus, which has led to outbreaks. Unlike other developed countries, Japan has never reported many cases among vaccine refusers. At the end of 2018, an unvaccinated measles patient joined a religious study camp for teenagers in Mie prefecture. Measles reports associated with that patient increased rapidly, and Mie prefecture requested FETP to support the outbreak investigation.

Cases were defined as either laboratory-confirmed or clinically diagnosed measles patients reported to Mie prefecture with report dates 7 January—1 February, 2019. We included clinically diagnosed cases because some cases refused testing at medical facilities due to their beliefs. We calculated descriptive statistics for case data that were collected by local health centers (e.g., demographic information, vaccine history, contact investigation) and attack rates. Genotype analysis by RT-PCR at Mie institute of public health was performed when possible.

A total 49 persons met the case definition, including 24 (49%) secondary cases associated with the camp. The median age was 17 years (IQR 14-22), and 55% were teens. Overall, 73% of cases and 83% of secondary cases were unvaccinated. Tertiary and quaternary case-patients were associated by family (36%), school (24%), and medical facilities (20%). The secondary attack rate at the religious camp was 71%. Among 42 cases with a specimen genotyped, all were D8.

This is the first measles outbreak response among a group of vaccine-refusers in Japan. Despite two-dose measles-containing vaccination coverage >95% in Mie prefecture, measles spread among the unvaccinated religious group with a high secondary attack rate. High vaccination coverage among contacts outside the religious group and quick response likely prevented the outbreak from spreading further or lasting longer. Therefore, we recommend achieving and maintaining high vaccination coverage nationwide to prevent secondary infections from non-vaccinated persons and the provision of more information on vaccines to vaccine refusers.

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