President Joe Biden's plan to share an additional 20 million COVID-19 vaccine doses overseas brings the U.S. total exports to 80 million. But experts and some policymakers say it's not enough. Driving the news: The world has reached a situation of "vaccine apartheid", World Health Organization director-general Tedros Adhanom Ghebreyesus said on Monday, saying "the big problem is a lack of sharing."Stay on top of the latest market trends and economic insights with Axios Markets. Subscribe for freeThe big picture: The low U.S. export numbers were at first defended as a strategy to ensure Americans are vaccinated first. But now the administration is being confronted by calls for a stronger involvement of vaccine diplomacy as domestic demand diminishes.80 million doses is a "drop in the bucket," and the U.S. should pledge to manufacture and export 4-to-5-billion doses by the end of the year, Peter Hotez, professor of pediatrics and dean of the National School of Tropical Medicine at Baylor College of Medicine, told CNN. G7 countries and the European Union can afford to donate more than 150 million vaccines to countries in need without compromising their own goals, UNICEF said on Monday.By the numbers: The U.S. has received more than four dozen requests for vaccine donations from countries across the world. China and Russia have exported larger shares of its vaccine production than the U.S., an analysis from Airfinity shows.China has shipped 252 million doses overseas, or 42% of its total production. The European Union has exported 111 million doses — more than a third of its total. Still, the announcement of 60 million doses was already a major boost to the severely strained global supply, Axios' Dave Lawler notes, considering the COVAX initiative has distributed about 45 million doses globally.Some Republicans — and Democrats — have become increasingly vocal in the U.S.’s vaccine diplomacy efforts, highlighting concerns lower-income countries are looking to U.S. competitors Russia and China for doses. "The U.S. should set a goal of vaccinating more than one billion people around the world by Thanksgiving—and without dumping intellectual property," Sen. Ben Sasse (R-Neb.) writes in a Monday op-ed to WSJ. Sen. Rick Scott (R-Fla.) tweeted: "I’m glad that @POTUS has answered my calls to distribute extra U.S. COVID vaccines to our allies across the globe. As the Administration crafts its excess vaccine distribution plan, I again urge them to consider the people of Venezuela and the Bahamas."What to watch: The administration has yet to announce how the doses will be shared or which countries will receive them.Like this article? Get more from Axios and subscribe to Axios Markets for free.