President Donald Trump’s decision to exit the World Health Organization means the U.N. agency is losing its biggest funder.

"Unfairly onerous payments" are cited in the executive order as a reason for WHO withdrawal. Countries’ dues are a percentage of their gross domestic product, meaning that as the world’s richest nation, the United States has generally paid more than other countries.

Tania Cernuschi, a WHO staff member of 10 years who has worked on improving vaccine access, said she thought of the campaign when she could not sleep after Trump's announcement.

WHO’s constitution, drafted in New York, doesn’t have a clear exit method for member states. A joint resolution by Congress in 1948 outlined that the U.S. can withdraw with one year's notice. This is contingent, however, on ensuring that its financial obligations to WHO “shall be met in full for the organization’s current fiscal year.”

The World Health Organization said Friday it was reviewing its priorities ahead of the withdrawal of its largest donor the United States, noting the agency provides vital services to protect against health threats.

The World Health Organization is drawing up a list of reasons why the U.S. should remain in the WHO for its own good, two sources familiar with the process told Reuters, as part of an attempt by its supporters to lobby incoming President Donald Trump.

GENEVA/LONDON -- The World Health Organization will cut costs and review which health programmes to prioritise after President Donald Trump announced he was withdrawing the U.S. from the WHO, the agency's chief told staff in an internal memo seen by Reuters.

The World Health Organization is drawing up a list of reasons why the U.S. should remain in the WHO for its own good, two sources familiar with the process told Reuters, as part of an attempt by its supporters to lobby incoming President Donald Trump.

By Patrick Wingrove, Jennifer Rigby and Emma Farge NEW YORK/GENEVA (Reuters) - The United States will leave the World Health Organization, President Donald Trump said on Monday, saying the global health agency had mishandled the COVID-19 pandemic and other international health crises.

If the U.S. withdraws funding and support from WHO, critical programs that support the survival of women and children will be at risk.

In this April 15, 2020 file photo, the logo and building of the World Health Organization (WHO) headquarters in Geneva, Switzerland.