In Japan, the spread of measles has reached alarming levels, marking the highest incidence since 2019. As of July 8, 2023, 547 individuals have contracted the virus, which is more than double the cases recorded in the entire previous year. Approximately half of these cases emerged in Tokyo, where health authorities are deploying a digital reporting system to swiftly interrupt new chains of infection.
The year 2019 witnessed a total of 744 infections, while Japan reported 265 cases in 2025, just 45 in 2024, and a mere 28 in 2023. Notably, during the peak of the current outbreak, Tokyo recorded 57 new infections in just one week.
Importation of Measles Viruses from Abroad
Genetic analyses conducted by authorities in Tokyo suggest that foreign tourists have introduced measles viruses into Japan. However, the majority of those infected contracted the virus domestically. Authorities believe that 397 of the 547 infected individuals acquired the disease in Japan, while 44 infections likely occurred abroad, and for ten cases, both possibilities are conceivable. The source of infection remains unknown for another 96 cases.
Since 2015, Japan has been classified as a country without sustained local transmission of measles. This status does not imply that infections do not occur; rather, imported viruses must not establish permanent infection chains. Japan successfully maintained this status until 2024.
In Tokyo, around 90% of those infected are 39 years of age or younger, which reflects the national trend where 82% of infected individuals belong to this age group. Younger patients, especially those experiencing mild symptoms, tend to leave their homes more frequently, thereby increasing the risk of transmission.
Vaccination Rates Fall Below Government Goals
Out of the 547 infected individuals, the vaccination status of 213 remains unknown. Among the infected, 80 individuals were unvaccinated, 77 had received one vaccination, and 177 had received both doses. The unvaccinated individuals and those with unknown vaccination status represent 53.6% of the cases. Alarmingly, the vaccination rate among Japanese children is below the government’s target of 95%. In the fiscal year 2024, 92.7% of children received their first regular dose, and 91% completed the second, a decline from 94.9% and 92% in the previous year.
The current vaccination regimen, which consists of two doses, was implemented in Japan in 2006. Many individuals in their late 30s and 40s had only the opportunity to receive one dose through the national vaccination program. Unverified claims regarding prevention circulate on social media, including statements suggesting that vitamin intake can protect against infection. A clinic director in Tokyo noted that such contradictory information might influence public behavior.
Unfortunately, there are no specific medications to treat measles. According to Japan’s Ministry of Health, almost everyone without immunity will contract the virus upon exposure. Approximately one in 1,000 infected individuals may develop encephalitis, and the mortality rate in industrialized countries stands at about one in 1,000 cases.
K-net Coordinates Infection Control Measures
Tokyo is utilizing the K-net reporting system to coordinate its response, linking all 31 health departments within the prefecture. K-net displays test results, as well as the locations and timestamps of infected individuals, providing a comprehensive overview. This system enables health departments to quickly identify individuals who have had contact with the infected.
During the COVID-19 pandemic, health departments exchanged much of their information via fax, which consumed personnel resources and hampered collaboration. K-net allows for faster dissemination of necessary information, particularly regarding measles cases among airplane passengers. Itaru Nishizuka, responsible for infection control coordination within the prefectural administration, indicated that information sharing during the pandemic sometimes took days, while K-net provides immediate accessibility for all involved parties.
Rapid Vaccination for Contact Persons
The system also aids in Tokyo’s rapid measles vaccination initiative. When health departments identify individuals who have come into contact with an infected person, they aim to vaccinate these individuals within 72 hours. Timely vaccination can prevent the onset of the disease.
Furthermore, Tokyo has established a dedicated network of motorcycle couriers for the transport of samples. Previously, health department personnel were responsible for delivering samples to laboratories themselves. Chika Takahashi from the Shinjuku health department stated that the new transport system has alleviated the burden. Multiple infections had occurred in a school within her jurisdiction, necessitating an efficient response.
