Countries thrashing out a historic agreement on tackling future pandemics must use the coming month for an extra round of emergency talks to bridge their differences, because failure cannot be an option, the co-chair for negotiations has said.

Nations have spent the last two years drafting an international accord on pandemic prevention, preparedness and response, but remain far apart on crucial issues such as vaccine equity and pathogen surveillance.

The planned final round of negotiations missed its target of finishing the accord by Easter, to make it ready for adoption by the World Health Organization's 194 member states at their annual assembly starting on May 27.