The U.S. accounts for 27% of the world’s coronavirus vaccine production, but 0% of the global supply beyond its own borders. Critics and allies alike say it’s time for that to change.

Why it matters: China has gotten a head start on vaccine diplomacy, sending millions of doses all over the globe, including to Latin America. Experts say it’s in America’s interests to compete in the race to vaccinate the world, and the calls to start doing so are getting louder.

Driving the news: The Biden administration took a tentative first step last week, offering around 4 million total doses of the Oxford/AstraZeneca vaccine — which isn’t authorized for use in the U.S. — to Mexico and Canada.

• The administration has also pledged $4 billion to the global COVAX initiative and more still to help increase supplies to Asia. But it’s holding tight to virtually every dose produced in the U.S.

"We're going to have excess supply," said Zeke Emanuel, vice provost for global initiatives at the University of Pennsylvania, who was a member of Biden’s coronavirus task force during the transition.

• "It would be unethical, and it would be a diplomatic and strategic mistake, to say we need to build up a buffer of 100 million doses while China and Russia are selling to people and saying, you know, 'You guys count,'" he tells Axios.

Where it stands: China has made about 33% of all the vaccine doses in the world. It’s exporting about 62% of its doses to other countries, which it can do, in part, because it largely has the virus under control domestically.

• The U.S. is the second-biggest producer, at 27%, but its bulk contracts with manufacturers keep doses produced in the U.S. from leaving.
• The global supply of the Pfizer/BioNTech vaccine is coming from the EU, which is exporting 48% of its production, vs. 0% from the U.S. according to Airfinity, a science information and analytics company.
• Moderna is using its European facilities to supply Canada with doses, because all doses produced at U.S. sites are going toward the 300 million the U.S. has purchased.

"It is a de facto ban" on exports, one European diplomat told Axios with some exasperation.

• The diplomat acknowledged that the U.S. had made early investments to ramp up supply, and thus should expect priority access — but expressed surprise that there was so little domestic opposition to Biden's "Americans first" approach.
• Leaders in Brussels are vigorously debating whether to tighten controls on exports from the EU, accusing the U.S. and U.K. of accepting imports while failing to reciprocate.
• Adar Poonawalla, the CEO of the Serum Institute of India, says the Biden administration’s applications of the Defense Production Act to steer supplies toward vaccine manufacturing in the U.S. are causing shortages elsewhere. India is exporting about 65% of the doses made there.

What's next: Most of the other major players will still be facing huge domestic needs long after the U.S. has secured enough doses for its entire adult population. That means the tap could soon be flipped on, allowing U.S.-made vaccines to flow all over the world.

• Emanuel expects that tipping point to come in June or July.
• Krishna Udayakumar, director of the Duke Global Health Innovation Center, said the U.S. could become the top exporter by the second half of the year.
• The U.S. has already purchased enough doses of approved vaccines to vaccinate 500 million people — more than enough for its entire adult population (roughly 250 million people) with plenty to spare for children and potential booster shots. Then there are 410 million additional doses from AstraZeneca and Novavax, which could be approved by May.

“The question really is, what is the threshold that’s going to satisfy the administration enough to allow the exporting of those doses?” Udayakumar says.

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