The Trump administration is asking Gavi, the Vaccine Alliance, to phase out the use of vaccines containing the preservative thimerosal if it wants future US funding.
Thimerosal is a mercury-containing preservative that’s been used in small amounts in some multidose vaccine vials since the 1930s to prevent microbial contamination. Although the preservative is no longer used in any routinely used US vaccines, it is used in some multidose vaccines in other countries.
US Health and Human Services (HHS) Secretary Robert F. Kennedy Jr. and many vaccine critics have long claimed that thimerosal is linked to developmental delays and neurodevelopmental conditions, including autism. Although those claims are not backed by evidence, in June 2025, a federal vaccine advisory board remade by Kennedy recommended that Americans receive only seasonal flu shots in thimerosal-free, single-dose formulations. (Multidose flu shots account for only a fraction of the US vaccine supply).
The World Health Organization (WHO) has concluded that the small amount of thimerosal, which contains ethyl mercury, in multidose vaccines does not cause harm.
The request, first reported by Reuters, suggests that US support for Gavi, a public-private partnership that helps provide and distribute vaccines to lower-income countries, may be contingent on the organization aligning itself more closely to Kennedy’s views on vaccines.
An HHS spokesperson said the United States has asked Gavi to submit a detailed action plan with a timeline for a phase-out of thimerosal-containing vaccines in its portfolio, a move they said would bring the poorest countries in line with US, Canadian, and European standards. But Gavi has not yet done so.
“Until a plan for removal of thimerosal-containing vaccines is developed and the plan initiated, the United States will withhold future new funding and pause access to the DFC [US International Development Finance Corporation] line of financing,” the spokesperson said.
US has been a longtime Gavi supporter
Launched by the WHO, World Bank, UNICEF, and the Gates Foundation in 2000, Gavi has vaccinated more than 1.2 billion children across 78 countries, preventing more than 20 million deaths from diseases like measles and pneumonia. The US government has long been a major financial supporter, contributing more than $8 billion since 2001. In 2024, the Biden administration pledged $1.6 billion to the organization over the next 5 years.
“The United States is deeply committed to this work,” former First Lady Jill Biden said in a statement announcing the pledge.
But the Trump administration announced early last year that it would terminate funding for the group. And in June 2025, Kennedy told Gavi leaders that the United States would withhold financial support from the organization until it has “re-earned the public trust” and starts taking vaccine safety seriously
“In its zeal to promote universal vaccination, it has neglected the key issue of vaccine safety,” Kennedy said in a pre-recorded video sent to Gavi officials and global health leaders who were in Belgium for a fundraising summit. “When the science was inconvenient, Gavi ignored the science.”
A demand based on ‘longstanding conspiracy theories’
Gavin Yamey, MD, MPH, Professor of Global Health and Public Policy at Duke University, called Kennedy’s accusations about Gavi baseless and said agreeing to the US demand “would be a massive setback for global vaccination and would impede kids from getting vaccinated.”
“It would cause enormous upheaval and could not be done suddenly, as it would require huge changes to the entire pipeline from manufacturing to supply and delivery, and there would need to be studies conducted of the safety and efficacy of using a different preservative,” Yamey told CIDRAP News.
Yamey explained that multidose vaccines, which allow many children to be vaccinated from one bottle, are particularly important for low-resource countries, because they cost less and involve simpler cold-chain logistics than single-dose vials. He added that the demand has no basis in data, science, or evidence, noting that over two decades of research has shown thimerosal is safe.
“It is a demand based entirely on RFK Jr.’s own longstanding conspiracy theories,” he said. “And it is children in low- and middle-income countries who will suffer the most from his appalling anti-science policies.”
A spokesperson for the medical humanitarian organization Medecins Sans Frontieres (MSF) said multidose vial shots like the diptheria, tetanus, and pertussis (whooping cough) vaccine are especially useful in the low-income settings and humanitarian emergencies where MSF works.
"Reducing the number of vaccines available through Gavi if they can no longer supply vaccines that contain thimerosal to ministries of health would block countless people all over the world from accessing these lifesaving tools," they said.
Reuters reports that the request would apply to $300 million in US funding that was requested by Biden and approved by Congress in 2024 and is still outstanding, as well as any future funding. The current congressional foreign assistance appropriations bill, which has been approved by the House of Representatives, includes $300 million for Gavi, but it still needs approval by the Senate and President Donald Trump.
It is a demand based entirely on RFK Jr.’s own longstanding conspiracy theories....And it is children in low- and middle-income countries who will suffer the most from his appalling anti-science policies.
Gavi did not respond to a request for comment, but a spokesperson told Reuters that any decision by the organization would “require a decision by Gavi’s board and input from preceding governance committees, which will be guided by scientific consensus.”
According to reporting last week by Devex, the United States no longer has representation on Gavi’s 28-member board because of the stalled funding.
Editor's note: This story was updated on February 2.
