The World Health Organization (WHO) is considering whether to use just one of the usual two doses of a cholera vaccine in Haiti to vaccinate more people, albeit with a shorter protection period.
The U.N. agency announced earlier this month that it would send 1 million doses of cholera vaccine to the Caribbean island. More than 200 cases of the deadly disease have been reported since Hurricane Matthew, and the numbers are expected to surge as the rainy season progresses between November and January.
The one-dose method will be 87.3 percent effective in reducing cholera for up to two months, according to a new study conducted in Juba, South Sudan, by Doctors Without Borders (MSF). The researchers administered the Shanchol vaccine to 160,000 people – the first time a single dose of oral vaccine had been used in a mass vaccination campaign.
“The results of the study are very promising,” said Iza Ciglenecki, MSF operational research coordinator, in a press release. “More research is needed, and we still don’t have full knowledge of the length of the coverage after two months. Nevertheless, this could be a milestone in cholera protection, as it may allow for the prevention of unnecessary illness and death during outbreaks. Given the lack of available vaccines, this is very good news.”
Cholera has a short incubation period, which leads to rapid outbreaks. But with this new approach, health organizations double their ability to reach vulnerable people in times of great need.
Effective cholera vaccines have been around for years, but the current vaccine options are either expensive or must be delivered in two doses, which is logistically challenging to implement during emergencies.
One such vaccine is Dukoral, which was widely used after its first licensure in 1992. It must be administered in two doses spaced weeks apart and diluted in 150 milliliters of clean water, making it difficult to use if clean water is in scarce supply.
The other widely available oral vaccine is Shanchol, which doesn’t need to be diluted, but does need to be administered in two separate doses. Given in two doses, the vaccine is 65 percent effective after five years. The caveat for Haiti is that the protection period is much shorter.
Still, some experts say the single-dose option is the best available. Delivering two doses of Shanchol to Haiti’s population of 10 million would cost $160 million, which health organizations say is not yet available. Even with adequate funding, the current global shortage of oral cholera vaccines also makes it impossible to vaccinate Haiti’s population; according to MSF, fewer than 4 million doses of oral cholera vaccine were produced in 2015.
The WHO and most other health organizations agree that vaccines cannot be the only solution to prevent the spread of cholera in Haiti. Peru resolved its cholera epidemic in the 1990s not by administering vaccines, but by improving sanitation and educating locals about personal hygiene. Many experts also stress the importance of building sewage treatment plants and a more resilient water system that can withstand natural disasters.
Cholera is an infectious disease spread through contaminated water. It causes severe watery diarrhea and dehydration, and can lead to death in just a few hours. In Haiti, the cholera epidemic was accidentally started in 2010 by U.N. peacekeepers who dumped infected sewage into a river, killing more than 6,000 Haitians and sickening more than 470,000 to date.