Here is the news article, written in the style of a senior financial correspondent.

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U.S. ultimatum to vaccine group: No more funds unless you stop using thimerosal

WASHINGTON – The United States government has delivered a high-stakes ultimatum to Gavi, the Vaccine Alliance, that threatens to disrupt immunization programs for millions of children in the world's poorest nations. This move escalates a rift between the U.S. and the global health community, placing billions in potential funding on the line over a scientifically discredited controversy.

In a direct challenge to the international public health consensus, the Department of Health and Human Services (HHS) has demanded that Gavi cease using the preservative thimerosal in the vaccines it distributes.

The consequence for non-compliance is severe: the U.S. will "withhold future new funding," according to a statement sent to NPR. The news, first reported by Reuters, marks a critical inflection point in global health policy, with the U.S. leveraging its financial might to enforce a domestic political agenda.

A Fractured Partnership

This ultimatum is the latest and most pointed development in a rapidly deteriorating relationship between the U.S. and one of the world's most impactful public health organizations.

The move follows a significant pullback in U.S. support. In June, the Trump administration rescinded over a billion dollars in previously pledged funds for the group. At the time, HHS Secretary Robert F. Kennedy Jr. accused Gavi of "ignoring the science" on vaccine safety, signaling a fundamental schism.

Now, the debate over thimerosal, a mercury-based compound, has become the administration's primary justification for threatening to sever future financial ties.

By the Numbers: The Stakes

The U.S. demand puts Gavi's vast and life-saving operations at significant risk. The organization's track record underscores the gravity of the potential funding shortfall.

• Gavi's Global Impact: Since its inception, the alliance has helped vaccinate over 1.1 billion children in lower-resource countries, a feat it estimates has prevented more than 18 million future deaths.
• Thimerosal's Role: Approximately 14% of Gavi's vaccine portfolio relies on multi-dose vials containing thimerosal. This includes critical immunizations like the 5-in-1 pentavalent vaccine, the DTP vaccine (diphtheria, tetanus, and pertussis), and the hepatitis B vaccine.
• U.S. Funding: The United States has historically been a cornerstone donor to Gavi, making the threat to withhold new funding a major blow to the organization's financial stability and long-term planning.

The Science vs. The Sticking Point

At the heart of the U.S. position is a long-debunked theory linking thimerosal to autism. Global health institutions and scientific bodies, however, are unified in their assessment of the preservative's safety and necessity.

• What It Is: Thimerosal is an ethylmercury-based compound that has been used since the 1930s as an antimicrobial agent in vaccines. Its purpose is to prevent the growth of dangerous bacteria and fungi in multi-dose vials.
• The Scientific Consensus: The World Health Organization (WHO), the U.S. Centers for Disease Control and Prevention (CDC), and the Food and Drug Administration (FDA) all affirm its safety. The WHO's advisory committee found "no evidence of toxicity in infants, children or adults exposed to thiomersal in vaccines."
• The Core Misconception: The controversy stems from conflating ethylmercury with methylmercury. Ethylmercury, the type in thimerosal, is processed and cleared from the body quickly. Methylmercury, found in some fish, is more toxic and can accumulate. As virologist Angela Rasmussen notes, the amount of mercury from a thimerosal-containing vaccine is less than that in a "tuna fish sandwich."

A Global Logistics Challenge

The U.S. demand overlooks the fundamental logistical and economic realities of vaccine distribution in the Global South, where thimerosal is not just a preference but a necessity.

The key difference lies in the packaging: single-dose versus multi-dose vials.

• Multi-Dose Vials: These vials, containing 5, 10, or more doses, are the backbone of immunization campaigns in low-income countries. They are significantly cheaper to produce and far more efficient to transport and store, a critical factor for nations with limited "cold chain" infrastructure—the network of refrigerators and freezers needed to keep vaccines viable. Thimerosal ensures these vials remain sterile as needles are repeatedly inserted.
• Single-Dose Vials: Predominantly used in wealthy nations like the U.S. and across Europe, single-dose vials do not require a preservative. However, they are more expensive and create a much larger physical footprint. "High-income countries can afford single-dose vials," explains Dr. William Moss of the Johns Hopkins Bloomberg School of Public Health. "But low-income countries have to maintain a cold chain and they just don't have the refrigerator space to be able to store the single-dose vials."

Forcing a switch would require a complete overhaul of Gavi's supply chain, introducing massive costs and logistical hurdles that could paralyze vaccination efforts.

The Bottom Line: Implications and What's Next

The U.S. ultimatum forces Gavi into an impossible position, with profound implications for global health.

• Humanitarian Impact: A disruption in funding or a forced, chaotic switch in vial type could halt vaccination campaigns. This would almost certainly lead to a resurgence of preventable diseases like diphtheria, tetanus, and hepatitis B, resulting in increased child mortality.
• Financial and Operational Strain: Gavi must now either scramble to replace a major source of funding or undertake a logistically nightmarish and prohibitively expensive transition away from a safe, effective, and essential component of its vaccine supply.
• Geopolitical Fallout: By prioritizing a domestic political issue over established science, the U.S. risks ceding its long-held leadership role in global public health. This creates a vacuum that other nations and philanthropic foundations may be pressured to fill, potentially reshaping the landscape of international health aid.

The global health community now watches to see how Gavi will navigate this financial and political minefield. The alliance's response, and whether the U.S. follows through on its threat, will determine the fate of immunization programs that have saved millions of lives and represent one of the greatest public health successes in modern history.