Geneva, Mar 12 (IANS): Another flu pandemic is inevitable and the world must prepare for potential devastation, the World Health Organisation (WHO) has said, warning that the risks must not be underestimated.

Launching on Monday its Global Influenza Strategy for 2019-2030, the world body said the next influenza pandemic "is a matter of when, not if".

WHO's Director-General Tedros Adhanom Ghebreyesus said it would be the biggest public health threat and potentially threaten millions of lives worldwide because of the rapid spread of viruses.

"The threat is ever-present," he cautioned.

Outlining the global strategy the WHO official said surveillance systems must be strengthened and better tools for prevention and containment of influenza virus should be developed, Xinhua news agency reported.

Chief of Influenza Preparedness and Response at WHO, Ann Moen said improved vaccines that have longer lasting immunity were needed, as well as antivirals and better treatment for the disease.

An estimated 1 billion people are infected with flu every year, leading to between 290,000 and 650,000 deaths, according to a WHO health report.

The last flu pandemic across the globe was caused by the H1N1 virus that spread around the world in 2009 and 2010. Studies found that at least one in five people worldwide were infected in 2009, and the death rate was 0.02 per cent.