Here are facts about U.S. financing for global health and potential implications of Trump's move, which could be followed by further cuts to international contributions.
BIGGEST DONOR
The U.S. contributes about 18% of funding for the WHO, which is struggling to raise cash for health emergencies from Gaza to Ukraine. The agency's two-year budget for 2024-2025 was $6.8 billion.
In that period, the U.S. financed 75% of WHO’s programme for HIV and other sexually transmitted diseases and over half of contributions to combat tuberculosis, the agency's data showed.
The U.S. is the world's top global health donor by far, giving $15.8 billion in 2022, according to Donor Tracker, a platform tracking development funding.
PANDEMIC TREATY
Trump is also sceptical about WHO-led negotiations for a post-COVID pandemic agreement aimed at improving global solidarity when the next health threat strikes.
Billionaire Trump ally Elon Musk has said nations should not "cede authority" to the WHO. The U.S. will cease negotiations on the treaty while its withdrawal proceeds.
GENEVA PERSONNEL
Trump's order also said that U.S. staff and contractors working with the WHO would be recalled and reassigned.
The United States Centers for Disease Control and Prevention (CDC) has worked closely with the WHO, seconding about 30 staff to Geneva and collaborating on research and outbreaks.
There are also a number of WHO Collaborating Centres in America.
DISEASE SURVEILLANCE
The U.S., like other WHO member states, is part of a global influenza surveillance network supervised by the WHO.
Among other things, the group advises on the composition of the annual seasonal flu vaccine.
Beyond its work with the WHO, the U.S. also funds many other global health programmes.
AIDS
The U.S. is a major funder in the fight against HIV. Much of that comes from PEPFAR, the U.S. President's Emergency Plan for AIDS Relief (PEPFAR).
It was only reauthorised by Congress for one year last year after conservative claims that some grant recipients promote abortion. That authorisation expires in March.
ABORTION
In his last term, Trump reinstated the so-called “Mexico City Policy”, requiring foreign charities receiving U.S. family planning funds to certify they do not provide abortions or give abortion advice.
He extended the policy, known by critics as the “global gag rule”, by cracking down on charities that fund other groups that support abortion. Trump also cut funding to the United Nations Population Fund (UNFPA), which works on reproductive health.
VACCINES
With vaccine-sceptic Robert F. Kennedy Junior nominated as secretary of state for health, the Trump administration's approach to vaccinations both domestically and internationally is unclear.
However, during Trump's last administration, contributions to the global vaccine group Gavi stayed roughly the same as under his Democratic predecessor and successor at the White House.
Funding also stayed at a similar level for the Global Fund to Fight AIDS, Tuberculosis and Malaria, another major global health player.
RESEARCH AND RESPONSE
Health agencies in the United States respond to emergencies and outbreaks worldwide, and also set norms and standards for medicines and safety through the Food and Drugs Administration and the CDC.
The National Institutes of Health is one the world's leading research centres and funds global health work around the world, from efforts to fight mpox to Ebola.
The global role of the U.S. in these areas under Trump is not yet clear, and will likely be led to an extent by events and priorities. For example, Trump set up Operation Warp Speed, to work on COVID-19 vaccines, during the pandemic.
