The expanding measles outbreak in Samoa that has so far killed at least 63 people comes amid a global surge in new cases, the World Health Organization and the U.S. Centers for Disease Control and Prevention said this week.

According to estimates, more than 140,000 people worldwide died of the disease last year — an “unacceptable number,” according to Henrietta Fore, UNICEF’s executive director, and the highest death toll in years. Preliminary estimates for this year indicate even higher figures.

In 2018, most fatal cases struck children younger than 5, the organization said, as fewer than 70 percent of children worldwide were estimated to have received a second dose of measles vaccine last year. A ratio of 95 percent would be needed to prevent the disease from spreading.

“The fact that any child dies from a vaccine-preventable disease like measles is frankly an outrage and a collective failure to protect the world’s most vulnerable children,” Tedros Adhanom Ghebreyesus, director general of the WHO, was quoted as saying in a release.

On top of that, a number of countries that used to be considered measles-free saw new sustained outbreaks in recent years, including Venezuela, Brazil, Albania, the Czech Republic, Greece and Britain.

But 2018′s surge to almost 10 million cases is driven by a smaller number of global hot spots, as measles is affecting some parts of the world far more intensely than others, the WHO said Thursday.

Sub-Saharan Africa has seen the worst impacts of the disease. Four out of the five countries that accounted for almost half the world’s measles cases last year — Congo, Liberia, Madagascar and Somalia — are in that region. The fifth is Ukraine, where a major outbreak began in 2017.

With a population of only about 200,000, Samoa has been similarly struck by the disease. Government authorities on the island nation said there have so far been 4,357 measles cases in this outbreak, which was officially declared Oct. 16. If the United States had Samoa’s current level of measles cases, there would now be more than 7 million infected Americans.

New Zealand’s “coffin clubs” — who work on coffins for themselves and others as a way of coping with death — have called on their volunteers to make baby coffins that will be donated to Samoan residents, amid reports that some families there cannot afford to bury their children.

More than one month into the outbreak, the CDC sent experts to Samoa to assist with the response in late November.

Whereas flawed health-care systems have been associated with surges in measles cases in some countries, the key reason for Samoa’s woes appear rooted in recent anti-vaccine activism, which pushed vaccination rates to dangerously low levels, partially because two nurses mixed vaccines with liquid muscle relaxant instead of water, which caused the deaths of two infants there in 2018. Even though the two responsible nurses were sentenced to prison, the country’s immunization coverage dropped below 40 percent that year, amid mounting distrust in government vaccination programs.

Now, in response, Samoa is starting to require vaccinations and to push back more forcefully against anti-vaxxers. Last month, the Samoan government declared a state of emergency and decreed immunizations compulsory.

On Thursday, Samoan authorities announced they also had arrested a man, Edwin Tamasese, over “incitement against the government” in response to anti-vaccine statements he had made, local media outlets reported.

According to Australia’s ABC broadcaster, Tamasese had traveled around the country to encourage families to not vaccinate their children. He was also active on social media, where his efforts were shared and supported by a Samoan-Australian social media influencer, among others.

“I’ll be here to mop up your mess. Enjoy your killing spree,” Tamasese reportedly wrote on social media in one instance, referring to the state’s immunization drive.

Authorities have also complained about U.S.-based anti-vaxxers trying to interfere in the government’s crisis response, Radio France Internationale reported.

Anti-vaxxers’ claims contradict scientific findings, as The Washington Post’s Ben Guarino, Neena Satija and Lena H. Sun have reported. Studies have disproved claims that vaccines — including those against measles, mumps and rubella — are connected to autism. A British physician who made such claims in a widely shared 1998 report was later struck off the medical register.

Many factors play into why anti-vaccination movements resonate around the world, regardless of the scientific evidence to the contrary. One common factor is a distrust of government and public health systems, which activists from different countries and communities draw on to link their movements.

In Pakistan, for example, the CIA tracked down Osama bin Laden in part by gaining information through an undercover polio vaccination team. That daring endeavor has subsequently fueled suspicion of anti-polio campaigns: Health workers running polio vaccinations have since been gunned down and kidnapped in Pakistan. Since bin Laden’s killing in 2011, there’s been a regional resurgence in polio, which at that time had been close to being eliminated, National Geographic reported.

In late November, in war-torn and mineral-rich Congo, a militia group attacked health-care workers providing vaccines against the recently resurging Ebola disease. U.N. peacekeepers posted nearby, meanwhile, were unable to stop the violence, as The Post’s Max Bearak reported.

In Congo, there’s a deep distrust of outsiders coming in to help the country, which is traumatized by decades of war and conflict over coveted resources. After many failed international interventions and responses, some have resorted to blaming foreigners for the country’s problems. That suspicion has made vaccination efforts for diseases such as Ebola and measles that much more dangerous and deadly, as there’s little public trust in those who say they’re there to help.

Despite the dire factors impacting growing suspicion of vaccines in parts of the world, there was also some good news related to 2018, the WHO said Thursday.

Compared with the beginning of the century, annual measles deaths have fallen significantly, from an estimated 535,600 in 2000 to 142,300 in 2018. There were also some new countries that had eliminated measles by the end of last year, including Austria, Oman, Timor-Leste, Singapore, Switzerland and Bahrain.

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