Cholera vaccine in the Caribbean: A hypothetical lifesaver

November 17, 2010

Richard Knox

(British Red Cross/Amanda George)
In Haiti, Widdline, 9, receives treatment from the Red Cross for her cholera like symptoms. Her father looks on.

The official count of cholera deaths in Haiti has surpassed 1,000 and authorities predict the disease will spread to other Caribbean countries.

There are two effective oral cholera vaccines that cost as little as $1 a dose. Could they prevent a lot of sickness and death in the coming months? Hypothetically. But don't bet the farm on it.

The problem, experts tell Shots, is there are only something like 500,000 doses of the vaccine on the entire planet. You read that right. There are only 500,000 doses of vaccine for a disease that sickens up to five million people a year and kills around 120,000.

What's more, since each person requires two doses, there's only enough cholera vaccine to immunize, at most, 250,000 people. And if you're also trying to protect young kids, who need three doses, then even fewer people can get protected.

And anyway, meeting the immediate threat assumes the entire world's stockpile could be airlifted in the foreseeable future to island of Hispaniola, shared by Haiti and Dominican Republic. Together their population is around 18 million.

Dr. Jon Andrus, deputy director of the Pan American Health Organization and an immunization expert, says PAHO recently "spent a lot of time discussing with some of the best experts in the world" whether to deploy cholera vaccine in Haiti and the Dominican Republic. There is a public health rationale for it, they decided.

But when they found out how pitiful the world's cholera vaccine stocks are, Andrus told Shots, "we dropped that discussion and didn't feel we needed to pursue it. There just wouldn't have been the supply. The question is: Who would you vaccinate?"

Or rather: Who would you deny the vaccine? It's not far-fetched to imagine vaccine riots.

Many public health experts say you can't use cholera vaccine during an epidemic to contain it. It moves too fast, they say. There are three infected-but-asymptomatic people for every obviously sick person, so you can't tell whom it's too late to vaccinate. It takes several weeks to vaccinate susceptible people and achieve effective immunity.

"If you're in the middle of a rip-roaring outbreak, the person you vaccinate would already have been exposed and the marginal gain from vaccination is not there," Andrus says.

Dr. John Clemens doesn't buy that. He's director-general of the International Vaccine Institute in Seoul, which developed one of the oral cholera vaccines with support from the Bill and Melinda Gates Foundation.

"There are a lot of assumptions made by people who say you can't really contain cholera with a vaccine," Clemens told Shots. "In fact, it's never been tried so we really don't know." He points out that current vaccines give considerable protection after the first dose.

However you come down on this debate, most would acknowledge there's a difference between containment and control. Containment means acting in the short term to keep a disease within a confined area. Controlling it means reducing the toll of illness and death over a longer period of time.

Haiti will soon transition from the acute outbreak phase to longer-term spread, within its borders and beyond. That's when cholera vaccine could really make a difference.

"There have been some studies to show that if you're in a community outside the outbreak and you have time to vaccinate, there might be a benefit," Andrus says, cautiously.

Although cholera is spreading rapidly in Haiti – so far six of the country's 10 provinces have been affected to greater or lesser degree -- there are still communities that have been relatively unaffected. And there will be time to make a difference for many.

Computer models "project about 200,000 cases over the next six to 12 months," Andrus said during a media teleconference Tuesday. Unless Haiti does a lot better at preventing death from cholera in the near term, we can predict that something like 10,000 people will die.

Moreover, Latin America's experience with a major cholera pandemic beginning in 1991 makes it "likely that cholera will spread to other countries in the hemisphere" in the foreseeable future, Andrus adds.

The University of Washington's Ira Longini says you don't have to vaccinate everybody to have a big effect. "Once you get 60 to 70 percent coverage, you shut off transmission of cholera," Longini told Shots. It's a well-known phenomenon called herd immunity.

But using vaccines to limit the disaster would require a massive increase in production of the two vaccines – Dukoral, made by a Dutch company, and Shanchol, a newer vaccine made by an Indian firm, Shanthal, that last year announced it was ready to turn out five million doses.

Even though there are only 250,000 or so doses of Shanchol that are ready to ship, Clemens of the International Vaccine Institute says there are many times that number available in bulk form. That vaccine could be shipped out if somebody stepped up and said we're going to do something big and bold to mitigate the Caribbean outbreak.

That would also take uncharacteristically fast footwork by the World Health Organization, which has not yet "prequalified" Shanchol – a seal of approval that clears the vaccine's purchase by agencies like PAHO.

Clemens says Shanchol "has been at the absolute back of the queue" for prequalification. "It's not even on the priority list for consideration, so certainly one thing WHO could do is move Shanchol up in the queue so it could be prequalified."

But the fundamental question is: Why is cholera vaccine in such short supply?

When Shots put that to Andrus he said: "It's hard to mobilize a commitment to produce medicines or vaccines to tackle diseases of poverty, disease of developing countries, where there might not be the profit you see with other diseases."

Longini was more blunt: "It's because of who's affected. Cholera is ignored because it's a disease of the poorest of the poor." Copyright 2010 National Public Radio. To see more, visit http://www.npr.org/.

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