The World Health Organization has reduced its management team by half and will have to scale back operations, its director-general said on Wednesday, four months after the United States announced it was leaving the agency and cutting funding.

"To be blunt, we cannot do everything," Tedros Adhanom Ghebreyesus said at a budget committee meeting ahead of the body's annual meeting next week.

President Donald Trump said the U.S. was leaving the agency on the first day of his return to office in January.

Under U.S. law, a one-year notice is required before the country, the biggest financial backer of the WHO, can leave, as well as the payment of all fees. That money is outstanding.

Tedros said the body and its member states must make difficult choices about what to prioritize, given a proposed 21 per cent cut in the budget for 2026-27 to $4.2 billion US.

Even that reduced budget will only be about 60 per cent funded, provided member states agree to raise their mandatory fees at the meeting next week, he said.

The WHO has already announced efficiency measures and hopes to save around $165 million US this year.

It will also reduce the number of its departments to 34 from 76 and plans to cut staff costs by 25 per cent, Tedros said, although that did not mean 25 per cent of jobs would be cut.

"But let's be clear: Reducing the scale of our workforce means reducing the scale and scope of our work," he said, adding the organization would close some offices in high-income countries.

Tedros said the WHO has had discussions with other global health groups to discuss better collaboration given the cuts.

The body's new leadership team of seven, including Tedros, is down from 14 people. The changes include moving chief scientist Dr. Jeremy Farrar into a role as assistant director-general for health promotion and disease prevention and control.

Dr. Chikwe Ihekweazu will become executive director of the health emergencies program, and Dr. Sylvie Briand will be chief scientist.