The United States on Wednesday rebuffed an appeal from the World Health Organization (WHO) for a moratorium on COVID-19 vaccine booster shots and for rich countries to focus instead on supplying poorer 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 sufficient supply to continue distributing shots abroad while also ensuring that every American can be fully vaccinated.

WHO 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 dose distribution between rich and poor nations.

More than 4.25 billion doses of COVID-19 vaccines have now been administered globally, according to an Agence France-Presse (AFP) count.

In countries categorized as high income by the World Bank, 101 doses per 100 people have been injected – with the 100 doses mark having been surpassed this week. That figure drops to 1.7 doses per 100 people in the 29 lowest-income countries.