Japan has recorded more than 400 measles cases since January 2025, according to the Japan Institute for Health Security, raising fresh public health concerns in a country that was declared measles-free just a decade ago. The outbreak is already significantly larger than the full-year total of 265 cases recorded in 2024, with months still remaining in the year.

Scale of the Outbreak

Medical institutions across Japan reported 68 measles cases in the week ending 26 April 2025, bringing the cumulative national total for the year to 436. By comparison, only 96 cases were recorded during the same period last year. The highest annual measles count Japan has seen in the past decade was 744 cases in 2019, a benchmark the current trajectory could approach.

Tokyo alone has accounted for 211 cases — nearly half the national total. When the neighbouring prefectures of Kanagawa, Chiba, and Saitama are included, the greater Tokyo metropolitan area has reported more than 300 cases in total, making it the clear epicentre of the current surge.

Who Is Most Affected

According to a notice issued by the institute in late April 2025, the majority of domestic measles patients this year are teenagers and people in their 20s. Notably, around half of those infected had either not completed the recommended two-dose vaccination schedule or had unclear vaccination histories — pointing to a significant immunity gap in younger age groups.

This pattern is consistent with global trends, where declining vaccination coverage in the post-pandemic period has left cohorts of adolescents and young adults under-protected against highly contagious diseases.

Why Japan Is Vulnerable Now

The World Health Organization (WHO) declared Japan measles-free in 2015, making the current resurgence particularly striking. However, since 2023, measles cases have been rising worldwide, increasing the risk of imported infections entering Japan through international travel. The institute has specifically flagged this imported-case risk as a key driver of the current outbreak.

Measles is among the most contagious infectious diseases known — the institute warned that more than 90% of non-immune individuals are likely to become infected after exposure to the virus. Severe cases can lead to life-threatening complications including pneumonia and encephalitis.

Health Guidance and Precautions

The institute has reiterated that receiving two doses of the measles vaccine remains the most effective means of preventing infection and severe illness. Travellers heading to countries or regions where measles is actively spreading have been advised to confirm their vaccination status before departure.

Individuals experiencing symptoms such as fever, rash, coughing, or conjunctival redness have been urged to contact medical institutions before seeking in-person treatment, and to inform healthcare providers of any recent overseas travel or contact with confirmed cases. With the outbreak still expanding, public health authorities are expected to intensify monitoring in the coming weeks.