SANAA, May 6 (Xinhua) -- The World Health Organization (WHO), in cooperation with Yemeni local health authorities, has launched a wide-scale anti-cholera vaccination campaign in south Yemen, WHO said in a statement Sunday.

It said the campaign will last until May 10, and targeted, in its first phase, four districts in Aden city.

The government-run Saba news website quoted deputy health minister Ahmed al-Waledi as saying that the campaign will include Tawahee, Mualla, Khormaksar and Sirah districts.

He said the oral vaccine would target nearly 350,000 children at the age of five.

Though the number of cholera infection cases has declined rapidly in the Yemen, fears grow about a possible new cholera outbreak in this rainy season, according to United Nations humanitarian agencies.

The rainy season began in April and will last until August.

In November 2017, the United Nations reported more than 925,000 suspected cholera cases with over 2,200 associated deaths in the war-torn country since the epidemic started in April of the same year.

The infection rate has since been declining, by around 0.2 percent to 0.3 percent, according to WHO.

Yemen has been locked in a civil war for more than three years between Iranian-allied Houthi rebel group and the internationally-recognized government backed by a Saudi-led coalition forces.

The war has killed more than 10,000 Yemenis, half of them civilians, and triggered the largest humanitarian crisis in the world.