The World Health Organization said Friday it had approved a South Korean company as the third producer of an oral vaccine against cholera, in a bid to double global stockpiles and address dire shortages.

The oral vaccine used to fight epidemics of the acute diarrhoeal infection, which can kill within hours due to rapid dehydration, is scarce and until now only used in rare cases to urgently stop the spread of the disease.

WHO said it had approved South Korean biopharmaceutical firm EUBiologics to make the vaccine, implying "a potential doubling of the available vaccine for this year," to six million doses, Stephen Martin of WHO's epidemic diseases unit told reporters in Geneva.

Last year, the sole contributor to the WHO stockpile, Indian firm Shantha Biotechnics, produced just three million doses -- enough to protect 1.5 million people with the necessary two-dose treatment.

Swedish firm Crucell also makes a WHO-approved cholera vaccine, but does not contribute to the stockpile, Martin explained.

He said the addition of the third producer was "very welcome", pointing out that last year "demand was greater than supply."

Both Sudan and Haiti made requests last year for WHO cholera vaccine supplies for pre-emptive immunisation campaigns, but were turned down due to the global shortage, the UN agency said in a statement.

Cholera is an acute diarrhoeal infection caused by eating contaminated food or water, with children facing a particularly high risk of infection.

There are between 1.4 and 4.3 million cases of the disease worldwide each year, and as many as 142,000 deaths.

Martin said the addition of a new producer would not only increase access to the vaccine, but was also expected to lower the cost per dose from $1.80 to $1.45.

And going forward, he said, "we expect to bring more producers to the market and to lower the price" further.

WHO first created its cholera vaccine stockpile in 2013, and since then more of the vaccines have been distributed and used than in the previous 15 years, it said.

A large portion of the vaccines used in 2015 went into a massive immunisation campaign in Iraq, where more than 2,800 cases of cholera were detected.

That campaign, which ended in December, focused especially on camps for refugees and internally displaced people, amid fears the disease would spread to war-ravaged Syria.

WHO said Friday the outbreak was considered to be over, and they had no indication Syria had been affected.