A nurse injects measles and rubella vaccine to a child during the immunization program in Yangon, Myanmar, Nov. 26, 2019. Myanmar's health authorities are conducting expanded immunization program against measles and rubella starting from Tuesday. Set to last until Thursday, the three-day program will cover children aged between nine months and 5 years old from a total of 234 townships across the country. (Photo by U Aung/Xinhua)

 
The World Health Organization (WHO) warned of a "slide back" in global efforts to eliminate measles on Tuesday, as the death toll from an outbreak that has killed dozens of children in Samoa continued to climb.

A total of 55 people have died since the epidemic began in mid-October, 50 of them children aged 4 or under, officials in the Pacific nation said Tuesday. 

Another 18 infants are critically ill in hospital and the crisis shows no sign of slowing, with 153 new cases in the past 24 hours, taking the national total to 3,881 in a population of 200,000.

WHO medical officer for the western Pacific, Jose Hagan, said it was a grim reminder of the danger posed by "probably the most infectious disease that we know of."

"Unfortunately the case [to] fatality rate of measles is much higher than people realize," he told Radio New Zealand. "This is quite a severe disease and we just aren't used to seeing it, so it comes as quite a surprise when we see how fatal it can be."

Hagen said increased access to measles vaccines was estimated to have saved 21 million lives over the past 20 years.

"But we are starting to have a slide back and there are outbreaks happening all over the world in all WHO regions and it's leading to the virus being exported through international travel," he said.

Cases have skyrocketed in Europe, leading to Britain, Greece, the Czech Republic and Albania all losing their measles-free status in August.

The US narrowly maintained its "measles eliminated" status a few months later, despite experiencing its worst outbreak since 1992.