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Toppage > Measles, Epidemiological week 1-10, 2026 (as at 11 March 2026)

Measles, Epidemiological week 1-10, 2026 (as at 11 March 2026)

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◆Measles, Epidemiological week 1-10, 2026 (as at 11 March 2026)

Measles is an acute viral infection caused by the measles virus and is characterized by high fever, generalized rash, and catarrhal symptoms. It is highly contagious and is transmitted primarily through airborne, droplet, and contact routes. Measles pneumonia, which commonly complicates infections in infants and young children, and measles encephalitis, occurring in approximately 1 in 1,000–2,000 cases, are major causes of measles-related mortality. In addition, individuals (mostly infants) who had measles and recovered may develop subacute sclerosing panencephalitis (SSPE) years to decades later. Although there is no specific treatment, measles is preventable through vaccination. Japan was verified by the Regional Verification Commission for Measles Elimination in the Western Pacific, World Health Organization (WHO), as having achieved measles elimination in 2015, and this status has been maintained through 2024. Maintaining elimination status requires high vaccination coverage, continuous measles surveillance, and rapid outbreak response. Under the Guidelines on Prevention of Specified Infectious Diseases Concerning Measles (MHLW Notification No. 442, 2007), maintaining elimination status remains a key national goal. This report summarizes the latest epidemiological situation of measles in Japan based on the National Epidemiological Surveillance of Infectious Diseases.

The number of measles cases reported during weeks 1–10 of 2026 (as at March 11, 2026) was 100, exceeding the number reported during the same period in any year from 2020 to 2025. Weekly case counts ranged from 0 to 5 cases per week during Weeks 1 to 4, and from 7 to 27 cases per week during Weeks 5 to 10, showing a marked recent upward trend. All 100 cases were laboratory-confirmed and met the pathogen-based diagnostic criteria required for notification. Among them, 71 were classified as typical ‘measles’, presenting all three clinical features (rash, fever, and catarrhal symptoms), while 29 were classified as ‘modified measles’, presenting one or two of these clinical features. There were 68 males and 32 females, with a median age of 28 years (range: 1–58 years).

Cases were reported from 20 prefectures. The prefectures with the highest number of reported cases were Tokyo (19 cases), Aichi (18 cases), Kanagawa and Niigata (10 cases each), and Osaka(9 cases). 67 cases (including 14 with unknown prefecture) were presumed to have been infected within Japan; 17 cases were presumed to have been infected overseas (Indonesia: 11; India: 1; South Korea : 1; Singapore: 1; Philippines: 1; Indonesia/Singapore: 1; Finland/Italy/France: 1); and the place of infection was unknown for 16 cases.

Vaccination history, as confirmed by medical institutions and public health centers, was analyzed by age group: 1–5 years (Age group that would have completed the first dose of routine MR vaccination) and ≥6 years (Age group that would have completed the second dose of routine MR vaccination). Among the 4 cases aged 1–5 years, 3 cases (75%) were unvaccinated, and 1 case (25%) had received one dose. Among the 96 cases aged ≥6 years, 17 cases (18%) were unvaccinated, 20 cases (21%) had received one dose, 25 cases (26%) had received two doses, and 34 cases (35%) had unknown vaccination status. Of the 25 cases with two documented doses, 13 cases were typical measles, and 12 cases were modified measles. All 20 unvaccinated cases were classified as typical measles.

As at March 11, 2026, measles virus genotype information was available for 57 of the 100 cases reported to the Infectious Agents Surveillance System. The detected genotypes were B3 in 45 cases (79%) and D8 in 12 cases (21%).

In recent years, measles outbreaks have been reported worldwide, and changes in the global epidemiological situation have been observed, including increased cases in Europe and the loss of measles elimination status in Canada. Even in Japan, which has achieved measles elimination, imported cases continue to be reported, leading to subsequent domestic infections . Individuals planning international travel should confirm the epidemiological situation at their destination, review their vaccination history, and receive any necessary vaccinations. In addition, within the country, several local governments have issued public advisories in response to cases of infection in schools and the occurence of patients at facilities where large numbers of people gather.

To prevent domestic transmission, completing the two-dose measles-rubella (MR) vaccination schedule under the Immunization Law remains the most important measure for both individual protection and maintaining herd immunity. Early case detection and rapid public health response are also essential. Key measures to prevent secondary transmission include accurate diagnosis, rapid contact tracing and response, and timely information sharing with healthcare providers and the public. Rapid communication between local governments is particularly important when patients travel widely or have contacts across multiple areas.

In areas where measles cases have been reported, and at medical institutions that may examine international travelers, infection prevention and control measures should be further strengthened. All healthcare personnel, including administrative staff, should have their vaccination and infection histories reviewed, and vaccination should be administered when necessary. Individuals who had contact with a measles case and develop symptoms such as fever should call the medical facility before visiting, and avoid using public transportation whenever possible to prevent secondary transmission.

Measles is an airborne disease and cannot be effectively prevented by hand hygiene and face mask use alone. It is highly contagious and infectiousness begins even before the onset of fever, and outbreaks have been reported in which a single measles case served as the index case, leading to an increase in the number of patients within the same facility or community. Continued occurrence of cases is therefore anticipated. In addition to rapid response, maintaining high two-dose MR vaccination coverage among children at the target ages for routine vaccination remains essential. Individuals without a history of measles or measles vaccination are encouraged to consult their healthcare provider regarding immunization.

International mass gathering events, including the 20th Asian Games (Aichi–Nagoya 2026), are scheduled this year and are expected to increase the potential risk of infectious diseases. Given the likelihood of contact with numerous unspecified individuals, especially in densely populated spaces, the verification of vaccination history is therefore recommended.

For detailed information and the latest updates regarding measles surveillance (as at March 11, 2026), please refer to the resources listed below:

 

Department of Infectious Disease Surveillance
National Institute of Infectious Diseases, Japan Institute for Health Security

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