“There is an incredible tension here given the supply remains constrained, and so far the U.S. efforts to expand global vaccine access have been woefully inadequate,” said Lisa Ouellette, a Stanford law professor who focuses on health law and the pandemic.

The U.S. has a strong domestic interest in expanding global access to Covid-19 vaccines, Ouellette said. But by further pushing boosters, “it will be harder to make the case to the public that it’s important to focus on global access,” she said.