The World Health Organization (WHO) on Tuesday adopted a long-awaited pandemic preparedness agreement aimed at strengthening global responses to future health crises. However, the absence of the United States, the WHO’s largest financial contributor, has raised concerns over the pact’s effectiveness.

Adopted at the World Health Assembly in Geneva after three years of negotiations, the legally binding agreement was greeted with applause from attending member states. It marks a major milestone for the global health agency following the fragmented international response to the COVID-19 pandemic.

WHO Director-General Dr. Tedros Adhanom Ghebreyesus hailed the agreement as “a victory for public health, science and multilateral action.” He said the pact will enable the global community to be better prepared and better protected when the next pandemic strikes.

Under the terms of the agreement, pharmaceutical manufacturers in participating countries will be required to allocate 20% of vaccines, medicines, and diagnostic tools to the WHO during a pandemic, to ensure timely access for lower-income nations.

Despite this milestone, the pact’s impact was tempered by the U.S.’s refusal to participate. The American delegation withdrew from the negotiations after former President Donald Trump initiated a process to pull the U.S. out of the WHO. Though President Joe Biden reversed that decision, U.S. engagement with the treaty remains absent.

U.S. Health and Human Services Secretary Robert F. Kennedy Jr. criticized the agreement in a video address to the Assembly, calling it a failure to address the shortcomings exposed during the COVID-19 crisis. “It has doubled down with the pandemic agreement which will lock in all of the dysfunction of the WHO pandemic response… We’re not going to participate in that,” he said.

The treaty was formally adopted after Slovakia, led by a vaccine-skeptic prime minister, called for a vote. A total of 124 countries voted in favor of the agreement, while 11—including Russia, Israel, Iran, Poland, Italy, and Slovakia—abstained. No country voted against the pact.

Global health advocates offered mixed reactions. Michelle Childs, policy advocacy director at the Drugs for Neglected Diseases initiative, welcomed the treaty’s focus on equitable access and research and development, calling it a potential game-changer for poorer nations left behind during the COVID pandemic.

Others were more cautious. Gian Luca Burci, academic adviser at the Geneva Graduate Institute’s Global Health Centre, described the agreement as “an empty shell” lacking enforceable commitments. “It’s a good starting point. But it will have to be developed,” he said.

Helen Clark, co-chair of The Independent Panel for Pandemic Preparedness and Response, praised the treaty as a foundation but warned that “many gaps remain in finance, equitable access to medical countermeasures and in understanding evolving risks.”

The pact will not come into full force until an annex outlining protocols for the sharing of pathogenic data is finalized. WHO said negotiations on the annex will begin in July, with hopes of reaching consensus within two years.