"We cannot simply carry on as we did before," Tedros Adhanom Ghebreyesus said as he opened the World Health Organization's annual assembly in Geneva.
WHO's member states have begun negotiations towards an international agreement aimed to ensure the world is better equipped to prevent or more effectively respond the next time a pandemic hits.
The process is still in the early stages, but the aim is for agreement to be reached in time for the next World Health Assembly, in May 2024.
"The pandemic accord that member states are now negotiating must be a historic agreement to make a paradigm shift in global health security, recognizing that our fates are interwoven," Tedros said at the start of the 10-day gathering.
That was also the message from a long line of other high-level speakers Sunday.
"I hope the current negotiations on pandemic prevention, preparedness and response result in a strong multilateral approach that saves lives," UN chief Antonio Guterres said, speaking via video message.
Timor-Leste President Jose Manuel Ramos-Horta meanwhile pointed out that "every country, big or small, rich or poor, struggled to mount an adequate response to the pandemic".
"This reminds us that we must build our house before the storm, not during the storm."