When it comes to a vaccine to prevent cholera, one dose may be as good as two. That is the finding of a new study whose authors say the strategy would make a new vaccine that is in short supply go further.
The World Health Organization is stockpiling 2 million doses of a recently licensed oral cholera vaccine to prevent the severe diarrheal illness.
An estimated 1.4 billion people around the world, according to the WHO, are at risk for contracting the water-borne illness, making the stockpile woefully inadequate to meet the need.
An outbreak of cholera often follows a natural disaster, when drinking water becomes fouled with human waste.
Single-dose effectiveness
In a new study, researchers looked at the cholera epidemic in Port-au-Prince, Haiti, following the 2010 earthquake. Roughly 120,000 people contracted the bacterial disease and more than 800 died.
But writing in the journal PLOS Medicine, they say if a single dose of the oral vaccine had been administered to the population within a year of the earthquake and the first reported cases, more than 78,000 cases of cholera might have been prevented and 783 deaths averted.
Justin Lessler, an epidemiologist at Johns Hopkins University’s Bloomberg School of Public Health, led the study looking at the effectiveness of a one-dose strategy. He compares it to the current vaccination protocol, which calls for giving a dose of the drug to those at risk, followed by a second dose, two weeks later.
“Even if a one dose isn’t 50 percent as efficacious as a two dose, it’s still the better strategy because when responding to an outbreak, the important thing is to get as much vaccine into the population as quickly as possible," he said.
Using a mathematical model, the researchers found that a vaccination campaign in Haiti using two doses would have protected five percent fewer people than the single-dose strategy.
Additional factors
Lessler said that outcome would be due to problems with refrigeration, as well as the effort of tracking down those who had received the first dose.
Investigators also analyzed the 2008-2009 cholera epidemic in Zimbabwe, saying almost 71,000 cases and 3,000 deaths might have been prevented.
“By using a one-dose campaign, you can protect the same number of people and protect them earlier, so you ultimately prevent more cases of the disease than if you’d used the two dose protocol,” he said.
Cholera, caused by the bacterium Vibrio cholerae, causes severe diarrhea that can lead to dehydration and death without immediate, supportive care. Children under five years of age are most vulnerable.
There is currently an outbreak in Juba, South Sudan, and only 250,000 doses of the oral vaccine are available.
Officials are testing the one-dose strategy in that region to see if they can limit cholera’s toll.
