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Current status of measles in Japan
Tetsuo Nakayama1, Jianhui Zhou, Motoko Fujino
1Laboratory of Viral Infection, Kitasato Institute for Life and Sciences, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641, Japan. tetsuo-n@lisci.kitasato-u.ac.jp
Abstract:
Approximately 20,000 to 30,000 cases of measles are reported annually in Japan, although the actual number of measles infections is considered to be five to ten times higher than the number of reported cases. Despite the availability of effective and safe live attenuated vaccines, regional outbreaks in Okinawa, transmission in adults, and secondary vaccine failures continue. Recent advances in molecular technology have contributed to molecular epidemiological studies, new concepts of asymptomatic infection, and the identification of different characteristics among measles virus genotypes. Measles virus strains isolated in Japan since 1984 were classified into the genotypes C1 (-1985), D3 (1985-1990), D5 (1990-1997), and Chicago-type D3 (1997-1999) from the results of sequencing the hemagglutinin gene. After 2000, the D5 genotype emerged, and, recently, the H1 genotype, which is now dominant, was introduced from Korea. Some of the currently circulating wild-types have different characteristics (high growth rate at 39 degrees C-40 degrees C). The cumulative vaccine coverage has reached 81%, but most measles cases involved unvaccinated individuals. Measles is a preventable disease and can be eradicated by increasing the vaccine coverage, and promoting the motivation for vaccination, in accordance with the worldwide measles strategy.
Insights
Measles outbreaks persist in Japan despite available vaccines, with evolving virus genotypes and vaccine failures. Increasing vaccination coverage is crucial for measles eradication efforts.
Area of Science:
- Virology
- Epidemiology
- Public Health
Background:
- Measles remains a significant public health concern in Japan, with high annual reported cases and an estimated higher true infection rate.
- Despite effective vaccines, challenges like regional outbreaks, adult transmission, and secondary vaccine failures persist.
- Molecular advancements enable detailed studies of measles virus epidemiology and genotype characterization.
Purpose of the Study:
- To analyze the molecular epidemiology of measles virus strains circulating in Japan since 1984.
- To understand the evolution of measles virus genotypes and their characteristics.
- To inform strategies for measles control and eradication.
Main Methods:
- Sequencing of the hemagglutinin gene of isolated measles virus strains.
- Classification of strains into distinct genotypes (C1, D3, D5, H1).
- Analysis of epidemiological data and vaccine coverage rates.
Main Results:
- Measles virus strains in Japan evolved through genotypes C1, D3, D5, and currently the dominant H1 genotype introduced from Korea.
- Circulating wild-type strains exhibit distinct characteristics, including a high growth rate at elevated temperatures.
- Most measles cases occur in unvaccinated individuals, despite an 81% cumulative vaccine coverage.
Conclusions:
- Measles virus evolution and specific strain characteristics pose ongoing challenges to control efforts.
- Vaccination remains the most effective strategy for measles prevention and eradication.
- Increased vaccine coverage and public motivation are essential to align with global measles elimination goals.