In short:
Donald Trump has signed an executive order to withdraw the US from the World Health Organization.
There are concerns the move could reverse progress made in fighting disease and increase pandemic risks.
What next?
Other countries may be forced to fill the funding gaps, with experts urging the world to collaborate on global health.Â
When US President Donald Trump was handed the folder with an executive order to withdraw from the World Health Organization (WHO), he exclaimed, "Ooh, that's a big one!"
Mr Trump has used his first days back in office to sign a flurry of executive actions.
Among them was a move that sets a 12-month notice period for the United States to leave the United Nations health agency and stop all financial contributions to its work.
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The US is by far the WHO's largest financial backer.
Experts fear the exit could roll back decades-long gains made in fighting diseases such as AIDS, malaria and tuberculosis.
It could also weaken the world's defences against new outbreaks capable of triggering pandemics.
Why Trump wants to withdraw from the WHO
Mr Trump has accused the WHO of mishandling the COVID-19 pandemic and other international health crises.
He said it had failed to act independently from the "inappropriate political influence of WHO member states" and required "unfairly onerous payments" from the US.
The changes Trump signed off on during his first day in office
Photo shows man signs paper at desk
He argued that US funding was disproportionate to the sums provided by other, larger countries, such as China.
"World Health ripped us off, everybody rips off the United States," Mr Trump said at the signing of the executive order.
"It's not going to happen anymore."
Mr Trump's withdrawal from the WHO was not unexpected.
He took steps to quit the body in 2020, during his first term as president, accusing the WHO of aiding China's efforts to "mislead the world" about the origins of COVID.
WHO vigorously denies the allegation and says it continues to press Beijing to share data on the discovery of coronavirus in Wuhan.
Mr Trump shows the crowd inside the Capital One Arena an executive order.  (Reuters: Carlos Barria)
The impacts on global health
The WHO is the UN's specialised health agency and is mandated to coordinate the world's response to global health threats, including outbreaks of mpox, Ebola and polio.
Explained: The story of the WHO
Photo shows An Ebola virus response team in protective gear.
It also provides technical assistance to developing countries, helps distribute scarce vaccines, supplies and treatments and sets guidelines for hundreds of health conditions, including mental health and cancer.
The US contributes about 18 per cent of the WHO's overall funding, which experts say was about $US1 billion ($1.6 billion) every year.
The organisation's annual budget is about $US6.8 billion.
Lawrence Gostin, a professor of global health at Georgetown University in Washington and director of the WHO Collaborating Center on National and Global Health Law, said the US withdrawal would "make the world far less healthy and safe".
"This is the darkest day for global health I've ever experienced," he said.
"Trump could be sowing the seeds for the next pandemic."
Part of the WHO's work includes vaccinating against diseases like polio, measles and cholera. (Reuters: Jorge Silva)
The WHO said that it regretted the move from its top donor country.
"We hope that the United States will reconsider, and we really hope that there will be constructive dialogue for the benefit of everyone, for Americans but also for people around the world," WHO spokesperson Tarik Jasarevic told reporters in Geneva.
Mr Trump's order said the administration would cease negotiations on the WHO pandemic treaty while the withdrawal was in progress.
US government personnel working with the WHO would also be recalled and reassigned, and the government will look for partners to take over necessary WHO activities.
US to be hit at home
Global health experts have suggested that the move could have major consequences for Americans.
In an interconnected world, if the US were to pull out of the WHO "they will lose considerably," Rob Moodie, professor of public health at the University of Melbourne, said.
"Because they have such dramatic inequalities, their level of health care is really very poor … Costa Rica and Mexico, in fact, have higher health indicators than most parts of the US," he told the ABC.
The COVID-19 pandemic killed more than 1 million people in the US. (AP: John Minchillo)
By leaving WHO, the US would lose its voice at the World Health Assembly, and the country and its many health agencies would lose access to critical health information.
Margaret Heffernan, a behavioural researcher with a focus is on Public health policy at RMIT University, said the US was shooting itself in the foot.
"The irrational withdrawal of the USA from the WHO now makes the USA vulnerable to decreased human capital and quality of life on all health indicators, lack of guidance on informed health emergencies, depleted health literacy and increase in non-communicable and communicable diseases," Dr Heffernan said.
"With USA international travel this potentially increases the disease risk for Australia making everyone globally vulnerable."
Other countries could 'step up'
The next-largest donor to the WHO is the Bill and Melinda Gates Foundation, although most of that funding goes to polio eradication.
Its chief executive Mark Suzman said on social media platform X that the foundation would continue to make the case to strengthen not weaken the WHO.
The next-largest state donor in terms of combined mandatory fees and voluntary contributions is Germany, which accounts for about 3 per cent of the WHO's funding.
Germany's health minister said on Tuesday Berlin hoped to talk Mr Trump out of the move.
The European Union voiced concern.
Experts say a collective response is crucial when dealing with outbreaks such as Ebola in West Africa. (Reuters: WHO/Junior Kannah/File photo)
Professor Moodie said Mr Trump's decision might force other countries such as China to "step up" and contribute more.
When asked about Mr Trump's executive order, China's foreign ministry told a regular press briefing that the WHO's role in global health governance should only be strengthened, not weakened.
"China will continue to support the WHO in fulfilling its responsibilities, and deepen international public health cooperation," Guo Jiakun, a ministry spokesperson, said.
Professor Moodie said it was essential that the world keeps working together.
The COVID-19 pandemic was an example of how collaboration was necessary address a global health crisis.
He said it demonstrated the importance of an organisation that can establish the baseline rules to help improve global health.
"There are a whole range of communicable diseases that need to be managed much more effectively by us working together, rather than just working in our country," Professor Moodie said.
"We cannot just sit in our own country and think that we can manage events just by literally turning inward."
ABC/Wires
