In announcing the one-jab change, the WHO said "The pivot in strategy will allow for the doses [available] to be used in more countries, at a time of unprecedented rise in cholera outbreaks worldwide."
The one-dose strategy had proved to be effective as a response to cholera outbreaks, the agency said, although the duration of protection is limited and appears to be much lower in children.
The U.N. agency said "the exceptional decision reflects the grave state of the cholera vaccine stockpile" at a time when countries like Haiti, Syria, Malawi are fighting large outbreaks of the deadly disease, which spreads through contact with contaminated water and food.
The WHO's emergencies director Mike Ryan told reporters the change in strategy was a sign of the "scale of the crisis."
A cholera outbreak in a north Cameroon refugee camp has killed three people and infected at least 36, the UN refugee agency said on Wednesday.
The first case was confirmed on Saturday in the Minawao refugee camp, which hosts around 75,000 people who fled Boko Haram insurgents in neighbouring Nigeria.