title: Assessing the transmission dynamics of measles in Japan, 2016.
abstract: Despite the verification of measles elimination, Japan experienced multiple generations of measles transmission following importation events in 2016. The purpose of the present study was to analyze the transmission dynamics of measles in Japan, 2016, estimating the transmission potential in the partially vaccinated population.
  
  
  
  All diagnosed measles cases were notified to the government, and the present study analyzed two pieces of datasets independently, i.e., the transmission tree of the largest outbreak in Osaka (n=49) and the final size distribution of all importation events (n=23 events). Branching process model was employed to estimate the effective reproduction number Rv, and the analysis of transmission tree in Osaka enabled us to account for the timing of introducing contact tracing and case isolation.
  
  
  
  Employing a negative binomial distribution for the offspring distribution, the model with time-dependent decline in Rvdue to interventions appeared to best fit to the transmission tree data with Rvof 9.20 (95% CI (confidence interval): 2.08, 150.68) and the dispersion parameter 0.32 (95% CI: 0.07, 1.17) before interventions were introduced. The relative transmissibility in the presence of interventions from week 34 was estimated at 0.005. Analyzing the final size distribution, models for subcritical and supercritical processes fitted equally well to the observed data, and the estimated reproduction number from both models did not exclude the possibility that Rv>1.
  
  
  
  Our results likely reflect the highly contagious nature of measles, indicating that Japan is at risk of observing multiple generations of measles transmission given imported cases. Considering that importation events may continue in the future, supplementary vaccination of adults needs to be considered.
authors.affiliation: Graduate School of Medicine, Hokkaido University, Kita 15 Jo Nishi 7 Chome, Kita-ku, Sapporo-shi, Hokkaido 060-8638, Japan; CREST, Japan Science and Technology Agency, Honcho 4-1-8, Kawaguchi, Saitama 332-0012, Japan. Electronic address: nishiurah@med.hokudai.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishiura
authors.affiliation: Graduate School of Medicine, Hokkaido University, Kita 15 Jo Nishi 7 Chome, Kita-ku, Sapporo-shi, Hokkaido 060-8638, Japan; CREST, Japan Science and Technology Agency, Honcho 4-1-8, Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Mizumoto
authors.affiliation: Graduate School of Medicine, Hokkaido University, Kita 15 Jo Nishi 7 Chome, Kita-ku, Sapporo-shi, Hokkaido 060-8638, Japan; CREST, Japan Science and Technology Agency, Honcho 4-1-8, Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Asai
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D007223:Infant; D007564:Japan / Q000453:epidemiology; D008297:Male; D008457:Measles / Q000453:epidemiology* / Q000635:transmission*; D008458:Measles Vaccine; D008875:Middle Aged; D055815:Young Adult
chemical_list: D008458:Measles Vaccine
keywords: Epidemic; Japan; Mathematical model; Paramyxoviridae; Statistical estimation; Transmissibility