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Toppage > Surveillance > Measles, Epidemiological week 1-13, 2025 (as at 2 April 2025)

Measles, Epidemiological week 1-13, 2025 (as at 2 April 2025)

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◆Measles, Epidemiological week 1-13, 2025 (as at 2 April 2025)

April 28, 2025

Measles is a highly contagious viral infectious disease transmitted by measles virus through airborne particles, respiratory droplets, and direct contact. Symptoms typically include a high fever, rash, and catarrh (i.e., cough, coryza and conjunctivitis). Measles can cause serious complications, with pneumonia and encephalitis being the two primary causes of measles-associated deaths. Additionally, persons (mostly infants) who had measles and recovered may develop Subacute Sclerosing Pan Encephalitis (SSPE), an encephalitis with poor prognosis that develops after an average incubation period of seven years. Although there is no specific treatment for measles and only symptomatic treatment is available, vaccination in advance can prevent measles. Japan was verified by the Regional Verification Committee for measles and rubella elimination in the Western Pacific Region, World Health Organization (WHO) as having achieved measles elimination in March 2015, and the current national goal for measles control is to maintain this status [Guidelines on Prevention of Specified Infectious Diseases: Measles (Ministry of Health, Labour and Welfare, 2007): https://www.mhlw.go.jp/content/000503060.pdf]. The aim of this article is to provide the most recent information on the epidemiology of measles in Japan, mainly based on the National Epidemiological Surveillance of Infectious Diseases.

As at 2 April 2025, 58 measles cases were reported in the first 13 weeks of the year, already exceeding the annual number of reported cases for each of the past five years (2020–2024). Since 2019, which saw the highest number of reported cases in recent years (378 cases in weeks 1 to 13), the numbers had remained low, partly due to the COVID-19 pandemic. However, an upward trend has been observed in 2025, beginning in week 8. The weekly numbers of reported cases were 1 case each in weeks 4-6, 3 cases in week 8, 4 cases in week 9, 12 cases in week 10, 14 cases in week 11, and 11 cases each in weeks 12-13.

Of the 58 reported cases, 57 (98%) were laboratory-confirmed cases that fulfilled the pathogen diagnosis required for notification. Among them, 50 were ‘measles (laboratory-confirmed)’ cases that fulfilled all three clinical symptoms required for notification (rash, fever and catarrh), and 7 were ‘modified measles (laboratory-confirmed)’ cases that fulfilled one or two of the three clinical symptoms required for notification. There was also one case (2%) of ‘measles (clinically diagnosed)’, in which measles could not be confirmed from laboratory tests, but all three clinical symptoms were fulfilled. There were 32 males and 26 females, and the median age was 26 years (range: 0-73 years). So far this year, 19 prefectures reported measles cases: 7 cases each in Tokyo, Kanagawa, Osaka and Hyogo; 5 cases in Saitama; 3 cases each in Chiba, Aichi, Yamaguchi and Fukuoka; 2 cases each in Gifu, Nara and Okayama; and 1 case each in Miyagi, Ibaraki, Tochigi, Gunma, Shizuoka, Shiga and Kyoto. The presumed place of infection was Japan for 18 cases (including 3 cases with unspecified prefecture), and abroad for 33 cases (25 cases in Viet Nam; 3 cases in Thailand; 2 cases in the Philippines; 1 case in Pakistan; 1 case in the Netherlands/Norway; and 1 case in Italy/France). The presumed place of infection was unknown for 7 cases. Regarding vaccination history collected by medical facilities and public health centers, 17 (29%) cases had no vaccination history, 10 (17%) had one dose, 12 (21%) had two doses, and 19 (33%) had unknown vaccination history. Of the 12 individuals vaccinated twice, 11 were laboratory-confirmed cases (9 measles, 2 modified measles) and 1 was clinically diagnosed. All 17 unvaccinated individuals were laboratory-confirmed cases (measles: 16 cases, modified measles: 1 case).

As at 2 April 2025, measles virus information was available for 30 of the 58 cases reported to the Infectious Agents Surveillance System. Of these, 25 cases (83%) were identified as genotype B3, 4 cases (13%) as genotype D8, and 1 case (3%) was not genotyped.

Measles outbreaks are currently being reported in Viet Nam and other foreign countries, and Japan is experiencing a rise in reports of imported cases associated with international travel. To help prevent both infection while abroad and the potential introduction of measles into Japan, travelers are advised to check the measles situation at their destination, review their vaccination history, and get vaccinated before traveling as necessary.

Within Japan, preventing measles virus transmission requires ensuring that individuals receive two doses of the routine measles-rubella (MR) vaccine, not only for personal protection but also to maintain herd protection. Furthermore, early detection of cases and rapid response are essential. As secondary transmissions from infected individuals to their contacts have been confirmed, appropriate diagnosis of measles, prompt contact tracing, and coordinated responses with relevant authorities are crucial. Timely communication with local medical institutions and raising public awareness are also key to effective prevention. When cases are likely to affect multiple areas, close information sharing between local governments becomes particularly important.

For medical institutions located in areas where measles has been reported or where there is a possibility of seeing individuals with overseas travel, it is important to reinforce measures to prevent nosocomial transmission. All hospital personnel, including administrative staff, should have their vaccination and infection history reviewed, and receive vaccination as necessary. Furthermore, if individuals who have been in contact with a measles case become aware of symptoms, they should call a medical facility in advance, inform them of the potential exposure, and avoid using public transportation to help 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 even before the symptoms appear, and there have been instances of transmission stemming from a single case. Given this, additional cases are likely to continue to occur. To prevent the spread of measles, it is crucial to respond quickly to new cases and to ensure that routine vaccination is up to date, especially for those who are eligible to receive two doses of the MR vaccine (children aged one year and those in the year before entering primary school). Individuals who have never had measles or received the vaccine are strongly encouraged to consult their medical doctor about vaccination.

EXPO 2025, commencing from 13 April this year, is an international mass gathering event and is expected to increase the potential risk of infectious disease outbreaks. Therefore, individuals are recommended to review their vaccination history, particularly for measles, given the expected contact with many people in crowded settings.

For further information and updates on measles, please refer to the following (cited on 2 April 2025, all articles in Japanese):

 

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

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