WASHINGTON, United States -- The United States on Wednesday rejected an appeal from the UN health agency for a moratorium on COVID-19 vaccine booster shots and for rich countries to focus instead on supplying poorer nations.

World Health Organization chief Tedros Adhanom Ghebreyesus had urged the countries and companies controlling the supply of doses to change course immediately and prioritize addressing the drastic inequity in vaccine distribution between rich and poor nations.

"We definitely feel that it's a false choice and we can do both," White House press secretary Jen Psaki told reporters, adding that the United States has donated more than any other country and was asking others to step up.

"Also in this country (we) have enough supply to ensure that every American has access to a vaccine," she added.

"We will have enough supply to ensure if the FDA decides that boosters are recommended for a portion of the population to provide those as well. We believe we can do both and we don't need to make that choice." The WHO has for months been sounding the alarm over a glaring and growing imbalance in vaccine availability against a disease that has killed 4.2 million people worldwide.

Some 4.3 billion doses of COVID-19 vaccines have been administered globally, according to an AFP count.

The WHO wants every country to have vaccinated at least 10 percent of its population by the end of September, at least 40 percent by the end of the year, and 70 percent by the middle of 2022.

In countries categorized as high income by the World Bank, 101 doses per 100 people have been injected. That figure drops to 1.7 doses per 100 people in the 29 lowest-income countries.A