By Jennifer Rigby

LONDON (Reuters) -A shortage of cholera vaccines is likely to last until 2025 as outbreaks surge worldwide, a global vaccine alliance said on Monday, days after the World Health Organization warned that the short-term outlook for controlling the disease was bleak.

Cholera cases and deaths jumped last year as the deadly disease spread to new regions, particularly conflict zones and areas with high levels of poverty.

In response, the World Health Organization and partners temporarily switched to using one dose of a vaccine that is normally given as two doses. But they still ran out last December.

The Gavi alliance, an international body focused on childhood vaccination, said in a report that there were currently enough doses to meet emergency demand but not for preventative use.

Cholera is spread by ingesting contaminated food or water, and while it often causes mild symptoms or none at all, serious cases cause acute diarrhoea and kill within hours if untreated. Access to safe water and sanitation are important to stop the disease, as well as vaccination and speedy treatment.

Balancing preventative vaccination campaigns with responding to urgent outbreaks has been challenging as case numbers have risen, global health organisations said.

Gavi said 48 million vaccine doses had been used in the last two years, 10 million more than in the entire previous decade.

It said supply should improve by 2026, as existing manufacturers ramp up and a new company enters the market, and called for better planning to ensure vaccines were used where they were most needed, including for preventative campaigns.

At a briefing on Friday, the WHO said 24 countries have reported outbreaks so far this year, compared to 15 last year. Case fatality rates are also higher than expected, the U.N. agency said.

"The outlook is bleak. We’re not able to provide enough vaccines," said Henry Gray, WHO's incident manager for the global cholera response, who said only 8 million of a requested 18 million doses had been made available in 2023.

(Reporting by Jennifer Rigby, additional reporting by Emma Farge, editing by John Stonestreet)