WHO cholera expert Dominique Legros told reporters in Geneva that the UN's global public health body had decided Monday to send the vaccines to the hurricane-ravaged Caribbean nation, to attempt to prevent an outbreak of the waterborne disease.
Hurricane Matthew wrought devastation as it made landfall in Haiti with 145 mile-per-hour (233 kph) winds a week ago, killing hundreds, displacing thousands, destroying homes and causing widespread flooding across the impoverished nation.
Legros said the flooding created a risk of "potential contamination of the drinking water by fecal sludge," leading to concerns about the "risk of further increase of cholera cases, particularly at that time of the year where over the last few years we have observed that there is a usual increase in cases reported between November and January."
Haiti has one of the highest rates of cholera in the world, with almost 10,000 people dead from the disease since 2010, when UN soldiers accidentally brought it to the country
in the aftermath of a major earthquake that year. The World Health Organization
reported 80,000 cases in Haiti since the initial outbreak -- and 770 new cases per week in 2016.
Haiti's interim President Jocelerme Privert told CNN Monday that the hurricane had accelerated the existing epidemic and undermined the strides made in fighting the disease.
"A lot of effort has been made to avoid the spread of this epidemic," he said. "But the hurricane has accelerated it."
Legros said the vaccines could cover 500,000 or a million people, depending on whether health officials opted for a "classic" two-dose strategy, or a single dose campaign, which would be easier to implement and would cover more people.
"The top priority clearly for those people affected by the hurricane is to give them access to safe water, that is the only way we can control cholera in the long term in Haiti," he said. Widespread damage to healthcare facilities in the hurricane-affected areas would also complicate efforts to treat cholera patients.
Cholera, which is spread through water or food contaminated with Vibrio cholerae bacteria, can cause severe diarrhea and vomiting, which leads to extreme dehydration. It can swiftly result in outbreaks, and patients who are not treated quickly can die within hours.
Before the hurricane, only 1 in 3 people in Haiti had access to proper latrines and less than 3 in 5 had access to safe water. In rural areas, these rates go down to 1 in 4 for sanitation and 1 in 2 for water. Diarrhea is one of the main killers of children under 5 in the country, UNICEF said.
Problem concentrated in devastated south
The uptick in cholera cases, confirmed and suspected, has been most apparent in the departments of Sud and Grand'Anse, on the southwestern tip of the country, according to the Red Cross.
Rene Domersant, Health Ministry representative at Haiti's National Emergency Center, told CNN there are currently 128 confirmed cases of cholera and at least 160 suspected cases in the departments of Sud, Grand'Anse and Nippes, which borders the former two.
The medical director of Haiti Air Ambulance, Dr. Vince DeGennaro, said there was "near total destruction" of towns he had visited by air along the southwest coast, and people were left with no option but to sleep outside.
In those conditions, he said, the threat of cholera was a "huge concern."
In Saint-Antoine Hospital in the devastated coastal city of Jeremie, in Grand'Anse, there were 43 suspected cases of cholera since the hurricane hit, hospital director Conception Panfillo told CNN's Ivan Watson Monday.
Conditions were poor at the hospital, which was badly damaged by the storm. More than 450 patients had arrived over the weekend, mostly people who had been wounded by flying debris, but the hospital had run out of anesthetics and antibiotics to treat them.
"We see a lot of helicopters and planes," Panfillo said. "But we haven't gotten any aid."
Don't drink the water
CNN spoke to Angela Joseph, one of several women trying to scrub their clothes clean in the potentially contaminated waters of the Grande-Anse River, which flanks the city.
Hurricane Matthew created a huge storm surge that swept through the area, killing her chickens and goats and leaving her and her three children with nothing to eat.
"I haven't eaten all day," she told CNN's Ivan Watson, as she washed clothes in a plastic bin.
Now the threat of cholera has made access to drinking water a problem too.
"Some people came and told us not to drink water from the river because of the cholera," Joseph said, adding that she would buy small plastic bags of drinking water when she could afford it.
'Nobody has to die' from cholera
WHO spokesman Christian Lindmeier said an exact number of cholera cases across Haiti is hard to estimate. Some cases can be mild, but when treatment is not available, the loss of fluids through diarrhea and vomiting can lead to rapid dehydration and shock.
"Cholera is a disease nobody has to die from. Eighty percent of people infected will only show mild symptoms, and it can be easily treated if people are properly hydrated," Lindmeier said.
The WHO warns that rebuilding health facilities is also a priority. Once the rainy season reaches Haiti in November, cases of cholera could rise even more steeply.
Despite the rise in the reported cases, Nadesha Mijoba, country director for Haitian Health Foundation, is hopeful that Haiti is better prepared than it was when the devastating earthquake struck six years ago.
"There is more awareness about cholera in Haiti today. Medical teams are trained on how to treat and identify the problem. In 2010, the Haitian people did not know what to do," she said.