Two dozen world leaders and the World Health Organization (WHO) on Tuesday called for the creation of a new international treaty to better prepare for future pandemics.

British Prime Minister Boris Johnson, South Korean President Moon Jae-in and Charles Michel, president of the European Council, joined WHO Director-General Tedros Adhanom Ghebreyesus in penning an op-ed urging for the creation of a treaty that would focus pandemic preparedness on the principle of health for all.

“There will be other pandemics and other major health emergencies,” the leaders wrote. “No single government or multilateral agency can address this threat alone. The question is not if, but when.”

The leaders said the coronavirus disease 2019 (Covid-19) pandemic has been the greatest global challenge since the 1940s and that they must come together to better prepare to predict, prevent, detect, assess and respond in a coordinated fashion to those that occur in the future.

“The Covid-19 pandemic has been a stark and painful reminder that nobody is safe until everybody is safe,” they wrote. “To that end, we believe that nations should work toward a new international treaty for pandemic preparedness and response.”

The main goal of the treaty would be to create a cohesive approach to dealing with pandemics that include strengthening national, regional and global capabilities as well as enhance cooperation on data-sharing, research and global production and distribution of medical and public health measures, vaccines and medicines.

The WHO has long called on nations, especially wealthy nations, to join its COVAX Facility that aims to provide equitable international access to vaccines.

The U.N. health body has also been highlighting how the current Covid-19 pandemic has exasperated pre-existing issues of inequality whether it be racial, economic and gender-based.

“At a time when Covid-19 has exploited our weaknesses and divisions, we must seize this opportunity and come together as a global community for peaceful cooperation that extends beyond this crisis,” they said.

Thailand Prime Minister Prayut Chan-o-cha, French President Emmanuel Macron and German Chancellor Angela Merkel are among the signatories.