Days before the United States may begin rolling out its vaccine booster program, the head of World Health Organization extended a previous call for a moratorium on giving boosters. The video shows WHO Director-General Tedros Adhanom Ghebreyesus speaking at a news conference Wednesday.

In August, Tedros urged countries to hold off on giving out boosters until the end of September. His newest call asks countries to wait “until at least the end of the year to enable every country to vaccinate at least 40% of its population” to begin giving boosters.

“Almost 90% of high-income countries have now reached the 10% target, and more than 70% have reached the 40% target,” Tedros said. “Not a single-low income country has reached either target. That’s not their fault.”

Right now, only Israel has begun giving boosters to large chunks of its population. However last month, U.S. health officials recommended all Americans get boosters pending FDA approval. Britain, Denmark, France, Greece, Germany, Spain and other countries have begun or are considering giving boosters to their vulnerable populations.

While WHO officials insist the scientific justification for giving boosters remains unclear, Tedros acknowledged that third doses might be necessary for at-risk groups. However, he also said “We do not want to see widespread use of boosters for healthy people who are fully vaccinated.”

Tedros also went after rich countries for what he describes as a failure to follow through on promises to donate doses. “High-income countries have promised to donate more than a billion doses, but less than 15% of those those have been materialized” Tedros said. “Manufacturers have promised to prioritize COVAX and low-income countries. We don’t want any more promises, we just want the vaccines.”

In response to this, White House Press Secretary Jen Psaki said the U.S. has donated and shared about 140 million doses with over 90 countries, “more than all other countries combined.”

“From Senegal to South Africa to India, we’ve made significant investments in boosting global productions of COVID vaccines,” Psaki said. “At the same time, the President and this administration has a responsibility to do everything we can to protect people in the United States.”

The Biden Administration’s goal is to start giving boosters by Sept. 20. However, research on its safety and efficacy is still underway.