The World Health Organization and other global agencies have launched the first oral cholera vaccination campaign in Yemen, aiming to reach millions of people in the war-torn country.
More than 2,200 people have died of the waterborne infection over the past year in Yemen, with another one million suspected cases across the country.
The first phase of the oral campaign targets more than 350,000 people in the southern province of Aden, according to a joint announcement by WHO, the United Nations children's agency UNICEF, the World Bank and the vaccine alliance Gavi.
After getting underway on Sunday, the campaign aims to reach Yemenis across the country, said Lorenzo Pezzoli, a cholera expert with WHO.
"It's an historical moment, it's the first time that the country uses this vaccine, to combat the devastating epidemic that started back in 2016," Pezzoli said in a WHO video published on Twitter.
Following vaccinations in Aden "the campaign will move towards all the areas at risk in the country, covering at least four million people," he added.
Research published this month in The Lancet Global Health journal warned cholera could still infect millions as the rainy season advances.
Based on data from previous outbreaks, researchers calculated that 54 percent of districts in Yemen could be affected by an epidemic flare-up in 2018, putting more than 13.8 million people at risk.
Cholera, which causes potentially deadly diarrhoea, is contracted by ingesting food or water contaminated with a bacterium carried in human faeces and spread through poor sanitation and dirty drinking water.
Left untreated, it can kill within hours.
The UN has described Yemen as the world's worst humanitarian crisis, with the country's conflict having a devastating impact on the population's health.
Some 10,000 people have been killed since March 2015 in the war between Saudi-backed pro-government forces and Iran-backed Huthi rebels in Yemen.
The conflict has pushed Yemen, the Arab world's poorest country, to the brink of famine.