This is what might happen if the US withdraws from the WHO

McKee thinks that the loss of funding will also affect efforts to eradicate polio, and to control outbreaks of mpox in the Democratic Republic of Congo, Uganda, and Burundi, which continue to report hundreds of cases per week. The virus “has the potential to spread, including to the US,” he points out.

“Diseases don’t stick to national boundaries, hence this decision is not only concerning for the US, but in fact for every country in the world,” says Pauline Scheelbeek at the London School of Hygiene and Tropical Medicine. “With the US no longer reporting to the WHO nor funding part of this process, the evidence on which public health interventions and solutions should be based is incomplete.”

Moss is concerned about the potential for outbreaks of vaccine-preventable diseases. Robert F. Kennedy Jr., Trump’s pick to lead the Department of Health and Human Services, is a prominent antivaccine advocate, and Moss worries about potential changes to vaccination-based health policies in the US. That, combined with a weakening of the WHO’s ability to control outbreaks, could be a “double whammy,” he says: “We’re setting ourselves up for large measles disease outbreaks in the United States.”

At the same time, the US is up against another growing threat to public health: the circulation of bird flu on poultry and dairy farms. The US has seen outbreaks of the H5N1 virus on poultry farms in all states, and the virus has been detected in 928 dairy herds across 16 states, according to the US Centers for Disease Control and Prevention. There have been 67 reported human cases in the US, and one person has died. While we don’t yet have evidence that the virus can spread between people, the US and other countries are already preparing for potential outbreaks.

But this preparation relies on a thorough and clear understanding of what is happening on the ground. The WHO provides an important role in information sharing—countries report early signs of outbreaks to the agency, which then shares the information with its members. This kind of information not only allows countries to develop strategies to limit the spread of disease but can also allow them to share genetic sequences of viruses and develop vaccines. Member nations need to know what’s happening in the US, and the US needs to know what’s happening globally. “Both of those channels of communication would be hindered by this,” says Moss.

As if all of that weren’t enough, the US also stands to suffer in terms of its reputation as a leader in global public health. “By saying to the world ‘We don’t care about your health,’ it sends a message that is likely to reflect badly on it,” says McKee. “It’s a classic lose-lose situation.”

“It’s going to hurt global health,” says Moss. “It’s going to come back to bite us.”

Update: this article was amended to include commentary from Pauline Scheelbeek.