As measles sweeps through Samoa, overwhelming health officials and killing at least 73 people so far, public health experts again find themselves doing battle with a vaccine-preventable disease. In a recent update, the World Health Organization called measles a “staggering global challenge” and called for increased vaccination to stem measles worldwide.

According to the latest figures released by the agency, almost half of last year’s measles cases came from five countries: Congo, Liberia, Madagascar, Somalia and Ukraine.

They’re not alone: In 2018, Albania, Czech Republic, Greece and the United Kingdom all lost their measles elimination status. (A country’s “eliminated” status is removed when the same strain of a disease has been continually transmitted within its borders for one year.)

Despite the continued presence of measles, which can be prevented through vaccination, the agency notes that vaccination rates have stagnated worldwide for nearly 10 years.

“Worldwide, coverage with measles vaccine is not adequate to prevent outbreaks,” the agency said in a statement.

The WHO adjusts its statistical models every year, resulting in new figures for 2018.

The agency estimates 9.7 million measles cases and 142,300 measles deaths last year. This year, however, the number of reported cases as of mid-November has risen threefold compared to the same time last year.

Most measles cases occur in the world’s poorest countries. But richer countries, such as the United States, are not immune.

This year, the United States almost lost its measles elimination status because of a nearly year-long measles outbreak in New York, and it had the greatest number of measles cases since 1992. The New York State Department of Health declared the outbreak over in October, and that month the Centers for Disease Control and Prevention announced it anticipated maintaining the country’s elimination status.

But the end of New York’s outbreak doesn’t mean the threat is over. Public health officials warn that measles cases are likely to continue being imported, and under vaccination places the United States “at continual risk” for measles outbreaks.