The first vaccine campaign against cholera in Yemen has started, the World Health Organisation (WHO) said on Monday, a year and a half after an epidemic was triggered by war and a health and sanitation crisis.
There have since been more than one million suspected cases of cholera in Yemen, and 2,275 recorded deaths, the WHO says.
The disease is spread by faeces in sewage contaminating water or food, and it can kill because patients quickly lose fluids through vomiting and diarrhoea.
Caught early it can be treated with oral rehydration salts.
The oral vaccination campaign, which began in four districts in Aden on Sunday targeting 350,000 people, coincides with the rainy season, which health workers fear could spread the disease further.
"The first four districts are being targeted ... and then the campaign will move towards all the areas at risk in the country, covering at least four million people," Lorenzo Pizzoli, WHO cholera expert, said in a tweet posted on Sunday.
Yemen's war, a proxy conflict between Iran-aligned Houthis and the internationally recognised government of President Abd-Rabbu Mansour Hadi, which is backed by a Saudi-led alliance, has killed more than 10,000 people since 2015.
It has also displaced more than 2 million and destroyed much of the country's infrastructure, including the health system whose workers have not been paid.
Nevio Zagaria, the WHO representative in Yemen, told Reuters in April that some 1.4 million vaccine doses had been shipped via Nairobi, out of 4.4 million planned.
"The rainy season is starting, so we need to use the window of opportunity to start a vaccination campaign," he said at the time.
In July 2017, the International Coordinating Group on Vaccine Provision - which manages a global stockpile - earmarked one million cholera vaccines for Yemen. But the WHO and local authorities together to scrap a vaccination plan on logistical and technical grounds.
Some senior Houthi health officials have been known to object to vaccinations, delaying the campaign, aid workers say.