Hundreds of thousands of doses of mpox vaccine that the United States had promised to send to African nations are in danger of going to waste, dozens of congressional Democrats said in a letter to the U.S. State Department on Wednesday.

Forty-eight Democratic members of the House of Representatives, led by Reps. Mark Pocan of Wisconsin and Sara Jacobs of California, signed the letter, saying that the vaccines may expire as they sit in warehouses, wasting the U.S. taxpayer dollars that paid for them.

The letter said 800,000 doses of the vaccines are at risk, and that some 220,000 doses could be viable if the State Department begins shipping them immediately.