The World Health Organization (WHO) on Monday outlined a global plan for fighting influenza and trying to prevent or slow any worldwide outbreak of the viral disease, warning that the danger of a pandemic was "ever-present."

"The question is not if we will have another pandemic, but when," said WHO Director-General Dr. Tedros Adhanom Ghebreyesus in a statement on the WHO website. "We must be vigilant and prepared — the cost of a major influenza outbreak will far outweigh the price of prevention."

Among other things, Dr. Tedros warned of the risk that a new influenza virus could transmit from animals to humans to trigger such a pandemic.

"With the partnerships and country-specific work we have been doing over the years, the world is better prepared than ever before for the next big outbreak, but we are still not prepared enough," he said. "This strategy aims to get us to that point."

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The WHO said there were an estimated 1 billion cases of flu each year, resulting in 290,000 to 650,000 respiratory deaths.

Strengthening national capacities

The United Nations agency recommends annual vaccinations to combat the disease, particularly for people working in health care and high-risk groups such as the old, the very young and those suffering from underlying illnesses.

The plan aims to build stronger national capacities to fight the disease, calling on countries to each have a special influenza program. It also wants to develop better tools for preventing, detecting, controlling and treating the disease and make these tools accessible for all countries. The anti-flu measures include vaccines and antiviral drugs.

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The world's last flu pandemic was in 2009 and 2010 and was caused by the H1N1 virus. At least one in five people across the world is thought to have been infected, with a mortality rate of around 0.02 percent, amounting to 18,500 deaths in 214 countries.​​​​​​​