From Science Magazine (AAAS):

1 million doses of a cholera vaccine, about half of the global supply, will be sent to Yemen with the vaccine being given out as early as July. But will it be enough? More than 20 million people live in Yemen and the government had asked for 3.5 million doses of the vaccine. Some of the world’s supply of cholera vaccine needed to be saved for other countries suffering from the disease.

Health workers have limited experience with the vaccine—which consists of killed bacteria and is given orally—in large emer­gency situations. The global stockpile was created only 4 years ago and has been used mostly for smaller campaigns. “How do we use the vaccine to stop an outbreak from spreading? We’re still learning,” says Melissa Ko of GAVI, the Vaccine Alliance in Geneva, which funds the stockpile. Experts have de­cided to stretch the supply by giving just one rather than the recommended two doses but are still debating where to target their efforts. And some caution that, because of the vaccine’s limited efficacy, even a plentiful supply might have only a modest impact on the massive epidemic.

The vaccine is a relatively new weapon, and until recently it was hardly used in emergencies. Many worried that immuniza­tion might distract aid workers from treat­ing patients and providing clean drinking water. Production capacity for the vaccine was limited as well, and the need to give two doses 2 weeks apart for optimal protec­tion created extra logistical problems. The speed at which cholera spreads made tar­geting the vaccine tricky: “We have seen on several occasions that we were too late or not in the right place,” says Dominique Legros, a cholera expert at the World Health Organization (WHO) in Geneva, Switzerland.

Cholera is spreading rapidly in Yemen with about 5000 new cases reported each day and over 200,000 since the epidemic started the end of April and over 1300 deaths. The vaccine will be stretched by giving only one dose instead of two. A single dose can provide 80% protection and is a good short-term solution. The research on this is still being conducted, but the WHO is open to the single-dose method.

For Yemen, it may simply be too little, too late, warns Renaud Piarroux, an infec­tious disease specialist at the University of Aix-Marseille in Marseille, France. By the time the vaccines are distributed, cholera may be everywhere, Piarroux says. “I will not say ‘Don’t do it,’ but I will not hope that it changes the course of the epidemic either.”

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