Japan is battling its worst measles outbreak in a decade, amid World Health Organisation (WHO) warnings that global efforts to halt the spread of the disease were failing, in part due to vaccine-skepticism.

More than 170 new cases have been recorded in Japan since the start of the year, according to public broadcaster NHK, affecting people in 20 of the county’s 47 prefectures.

The number of new cases over that period is the highest for 10 years, with 49 recorded in the central prefecture of Mie, followed by Osaka with 47, the National Institute of Infectious Diseases said.

More than half of the cases in Mie involved members of the religious group Kyusei Shinkyo who had attended a workshop late last year. The group believes that medicines are “harmful” and advocates purification of the body and spirit. It later apologised for the outbreak on its website and said it was cooperating with health authorities.

Japan’s health ministry urged people to get vaccinated immediately and hospitals and other medical facilities to take preventive measures.

Measles is a highly contagious disease that can cause severe diarrhoea, pneumonia and loss of vision. It can be fatal in some cases and remains an important cause of death among young children, WHO said. The disease can be easily prevented with two doses of a safe and efficient vaccine that has been in use since the 1960s, it added.

Earlier this month the WHO cited vaccine-skepticism, conflict and poor access to healthcare in some regions for a 50% increase in measles cases worldwide last year, including in developed countries where vaccination coverage has historically been high.

“Our data are showing that there is a substantial increase in measles cases. We’re seeing this in all regions,” Katherine O’Brien, the UN agency’s director of immunisation, vaccines and biologicals, told reporters in Geneva. “We’re having outbreaks that are protracted, that are sizeable and that are growing. This is not an isolated problem.”

Experts have partly attributed the rise in cases in developed countries to complacency and baseless claims linking the measles vaccine to autism.