Publisher Health

A record number of cholera outbreaks around the globe, driven by droughts, floods and armed conflicts, has sickened hundreds of thousands of people and so severely strained the supply of cholera vaccines that global health agencies are rationing doses.

Outbreaks have been reported in the Caribbean, Africa, the Middle East and South Asia, putting the health of millions at risk and overwhelming fragile health systems. Untreated, the disease, which is commonly spread through contaminated water, can cause death by dehydration in as little as one day, as the body tries to expel a virulent bacteria in gushes of vomit and watery diarrhea.

Cholera is typically fatal in about 3 percent of cases, but the World Health Organization says it is killing at an accelerated rate in recent outbreaks, even though it is relatively cheap and easy to treat. It is most often fatal in children, who progress swiftly to severe illness and organ failure.

Cholera outbreaks tend to follow displacement: When droughts, floods, famines or the threat of violence force large groups of people to move, and they lose access to clean water and adequate sanitation facilities, cholera bacteria can race through a population. This year has seen cholera both in places where it is a familiar threat, and in countries that have not confronted it for decades.

“The situation is very concerning, very worrying,” Dr. Philippe Barboza, who leads the World Health Organization’s cholera response, said. “We have had to worry about war and poverty and population movements, and that has not changed. But now we have climate change on top of that.” He called the profusion of cholera outbreaks “a fire that is just going to keep getting bigger.”

In Nigeria, a million people have been displaced by floods in recent weeks, and there are at least 6,000 cases of cholera. The authorities in Kenya are reporting suspected cholera in people fleeing violence in Somalia and arriving at the mammoth Dadaab refugee camp, where tens of thousands of children are at risk.

In Haiti, cholera has broken out as whole neighborhoods of people displaced by violence are packed into small open patches in Port-au-Prince, sharing a single cracked pipe of water that runs through untreated waste. Cholera is also festering in the country’s severely overcrowded prisons.

In Syria, millions of people displaced by the civil war lack access to clean water, while the years of fighting have destroyed sanitation infrastructure. Raw sewage is being pumped into the Euphrates River, which hundreds of thousands of people depend on for water. The United Nations reports more than 20,000 suspected cholera cases and 75 deaths there.

In Pakistan, where a third of the country is fully under water after massive monsoon flooding, and close to 10 million people have been displaced, there are reports of cholera cases in a dozen locations. These are not yet full-blown outbreaks, and vaccination could help stave off disaster.

But demand for vaccination is so high that the World Health Organization has suspended the recommended two-dose vaccination regimen and switched to a single dose, in an effort to stretch supply so enough is available to be able to respond to more outbreaks that could occur in the coming months.

“We have never had to make a decision like this about vaccination before, that’s the severity of this crisis,” Dr. Barboza said.

If enough single doses are given in a region, it should be enough to quell an outbreak, she said. But the length of the protection is significantly shorter. A single dose of the cholera vaccine gives between six months and two years of immunity, while the full regimen of two doses delivered a month apart gives adults four years of protection, she said. If a second dose can be delivered within six months, it should give three years of protection. But the evidence on the exact duration of protection is limited; it is known to be much shorter in children.

Some 36 million doses of the oral cholera vaccine were expected to be produced in 2022, and of those, 24 million have been shipped for vaccination campaigns. The remaining eight million doses have already been designated for a second round of emergency vaccination in four countries — Cameroon, Malawi, Pakistan and Kenya — the W.H.O. said.

That prompted the coordinating body that allocates cholera vaccines to decide to switch the vaccination regimen to a single shot until new supply is available, most likely by the end of the year. (That body is made up of the W.H.O., UNICEF and the aid organizations Médecins Sans Frontières and the International Federation of Red Cross and Red Crescent Societies, which staff cholera emergency centers around the globe.)

Dr. Seth Berkley, the chief executive officer of GAVI, a nongovernmental organization that manages the global stockpile of vaccines for cholera among other pathogens, said that he believed as many as five million doses would be produced through the end of 2022 and that some existing requests would be canceled, so that 12 million doses could still be available this year.

Dr. Daniela Garone, M.S.F.’s international medical coordinator, said the vaccine demand had left the agencies to make grim choices. “It leaves you sitting at a table literally having to have conversations like, well, do we send it to Haiti or do we send it to Syria?” she said. “Do we send it to Zimbabwe?”

Ideally there would be regional vaccination in southern Africa right now, Dr. Garone said. For example: An outbreak in Malawi threatens neighboring countries because there is a lot of movement of people across borders with Zambia and Mozambique. But there are insufficient supplies to do that kind of preventive campaign in the region, or in India, Pakistan, Nigeria or the Democratic Republic of Congo.

“There is just not enough vaccine,” she said. “And it’s the chicken or the egg: Do you prevent or you react? At the moment we are only on the reacting, trying to prevent mortality, and we cannot prevent.”

A cholera vaccination campaign does not aim to cover the entire population of a country, but rather the area around a hot spot of transmission. The primary goal is to buy a country time to put sanitation measures in place, such as setting up latrines and trucking in sources of clean water, that are key to stopping transmission.

The bulk of the world’s cholera vaccine is made by a South Korean company called EuBiologics. Some 15 percent of the global stockpile was produced by Shantha Biotechnics, a wholly owned Indian subsidiary of the French drugmaker Sanofi, but the company decided two years ago to stop production of its cholera vaccine by the end of this year and end supply by the end of 2023. That planned exit from the market coincides with the spike in demand.

Dr. Barboza said that EuBiologics was producing at capacity and working to expand its production, and that another drugmaker would soon begin to produce the vaccine.

“But even a sharp increase in production will be low compared to the need,” he said.

Drugmakers in high-income countries have little interest in making the vaccine, which typically sells for about $1.50 a shot, Dr. Barboza said. “It’s a marker of vulnerability and poverty and will never affect a rich country not at war.”

A second problem is that the funds to buy more cholera vaccines often come out of the same limited envelope allotted for the drinking water and sanitation work that is necessary in an outbreak, said Gian Gandhi, the chief of health emergencies strategy for UNICEF’s supply division.

While the global cholera case count is high, death numbers, at the moment, remain relatively low, which reflects the fact that cholera treatment is relatively cheap and simple. “Even countries that have not been exposed to cholera before, they can learn quickly,” Dr. Garone said.

The International Center for Diarrheal Disease Research, Bangladesh hospital, where the cholera treatment was pioneered and which played a key role in the development of the vaccine, saw a record number of cholera patients in March and April this year. Instead of a typical 400 patients a day, the hospital treated 1,500, most of them in giant tents erected outside the facility to absorb the crowds, Dr. Ahmed said. There, the driver was not flood but heat: Extreme temperatures led to large-scale population movement, leaving people without clean water.

But only a few people died, he said, because simple oral rehydration salts and antibiotics will cure most cases. Then, to help end that outbreak, more than two million people were vaccinated using contact tracing to hot spots. Bangladesh has been working toward preventive vaccination in known cholera flashpoints in an effort to keep outbreaks from starting.

Dr. Berkley said that currently 85 percent of the supply was being used in emergencies. “If you could go in and do preventive vaccination in these hot spots, you could blot out these different places that are where the disease is transmitted from,” he said.

Dr. Barboza said that while cholera outbreaks were difficult to predict, the W.H.O. anticipates that there will be more, because of climate change. While flooding disasters such as those in Nigeria and Pakistan right now immediately evoke fears of cholera, the risk from drought can be even greater, he said.

“When water is scarce you can have people packed even more closely, perhaps all using a single spring that is not protected, and more people means more risk of contamination,” he said. “They don’t have water to wash, or to wash their vegetables, and it’s a spiraling effect.”

If some of the outbreaks underway now continue past six months, the immunity of the people vaccinated with just one dose will have waned, and they will need to be revaccinated, he said. Ideally that would be with the full two-dose regimen, if supplies have been built back up. But, he added, the same factors driving outbreaks — insecurity and floods — make it hard to vaccinate.