Almost 5,000 people have been struck by a measles outbreak in the small Pacific island nation of Samoa, where authorities have declared a state of emergency, imposed compulsory inoculation and arrested an anti-vaccination campaigner.

As the death toll in Samoa rose to 70, with most of the victims children, the World Health Organization issued new estimates showing that measles deaths worldwide rose to 140,000 in 2018.

How did an infectious disease that was on the way to global eradication resurface as a health emergency?

The WHO and other international agencies blame stagnating rates of child vaccination, a trend driven by anti-vaccine propagandists persuading a growing number of parents that the treatment is unsafe.

"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," according to Tedros Adhanom, WHO director-general, an Ethiopian whose brother died in childhood from suspected measles.

The anti-vaccine movement was spawned on the internet in developed countries such as the United Kingdom and United States from the turn of the century. But it has now spread to areas of the developing world where it is doing the most damage.

The WHO says the most affected countries in 2018 were the Democratic Republic of the Congo, Liberia, Madagascar, Somalia and Ukraine.

The anti-vaccine message has compounded an existing problem in areas of unrest and conflict where access to health systems was already disrupted.

The anti-vaccine activist arrested in Samoa was charged with campaigning against vaccines on Facebook and proposing ineffective remedies such as papaya leaf extract and vitamin C.

Elsewhere, four European countries previously declared to have eradicated the disease, the UK, Albania, the Czech Republic and Greece, this year lost their measles-free status, according to the WHO.

The initial vaccine scare was ignited in a 1998 paper by the now disgraced UK physician Andrew Wakefield, who claimed a link between the measles, mumps and rubella vaccine and autism.

Although the claim was subsequently debunked by experts and exposed as an elaborate fraud by his peers, the vaccine conspiracy continues to thrive online alongside Wakefield's continued denials that his findings were wrong.

And in countries such as the US, where authorities have taken measures to ensure the vulnerable young are vaccinated, the movement has spread to the streets where doctors and parents have faced intimidation and threats from anti-vaccine campaigners.

The United Nations children's charity UNICEF estimates more than 20 million children a year worldwide are now missing out on the first dose of the measles vaccine even as rates of the disease in some areas tripled this year.

"The measles virus will always find unvaccinated children," according to Henrietta Fore, UNICEF executive director. "If we are serious about averting the spread of this dangerous but preventable disease, we need to vaccinate every child, in rich and poor countries alike."

The US topped the table of high-income countries where the most children missed out on their first measles jab-more than 2.5 million between 2010 and 2017-followed by France and the UK.

Vaccination rates in the US are at around 91 percent compared with China, at the other end of the scale, which has a 99 percent rate of vaccination.

China historically suffered relatively high levels of measles but, despite continued isolated outbreaks, is now seen as on course toward elimination of the disease.

Elsewhere, studies have shown a variety of motives behind the phenomenon.

It turns out that not all those who choose not to inoculate their children are conspiracy theorists. In countries where measles and other preventable diseases are now relatively rare, people have become complacent about the need to protect their families.

Researchers have found that parents looking for information on vaccination online are more often than not driven to anti-vaccination websites.

A study in 2017 revealed that anti-vaccine messages were rife on the Twitter social media site, with many of the postings propagated by affluent young mothers.

The anti-vaccine trend appears to be fostered in part by a general suspicion of the wealthy pharmaceutical industry despite assurances from health professionals that any vaccine must be rigorously tested to ensure the benefits outweigh any risks.

The WHO has listed vaccine hesitancy among its 10 biggest threats to global health in 2019 and stressed the need for more trusted, credible information on vaccines.

A group of researchers from France and the UK put the situation even more starkly. They noted that all vaccines were collectively responsible for saving at least five lives every minute. If more people had their jabs, the world could avoid an estimated 1.5 million deaths annually, the equivalent of eight jumbo jets crashing every day.

Harvey Morris is a senior media consultant for China Daily UK