Haiti's ministry of health and international aid organisations are launching a cholera vaccination campaign on Tuesday.
Their aim is to vaccinate about 820,000 people within a week.
The campaign comes after a rise in cholera cases following the devastation caused by Hurricane Matthew, which hit the country on 4 October.
Cholera has killed around 10,000 people since 2010, when UN peacekeepers introduced it to Haiti.
Last August, the UN acknowledged it had played a role in the outbreak after scientific studies showed that Nepalese UN troops were the source of the disease.
The troops had emptied toilet waste into the Meille River, a major water source.
The vaccination campaign is believed to be one of the largest of its kind after a natural disaster.
One million doses of the vaccine were shipped to Haiti ahead of the campaign.
Thousands of health workers will administer the oral vaccine to people in 16 communities in the provinces of Grande-Anse and Sud, which were worst hit by Hurricane Matthew.
According to UN figures, the number of suspected cholera cases in Haiti rose to about 3,000 in the wake of the hurricane.
Experts warn that the vaccine is not a complete solution.
They say that one dose is about 65% effective for a period of six months.
Health workers delivering the vaccines will also provide advice on how to prevent the spread of cholera.
They say hand washing, chlorinating the water and washing food are key.