To send more vaccines overseas, the U.S. seeks to replace the millions of AstraZeneca doses still under review.

To meet its global vaccines pledge, the U.S. seeks to replace the millions of AstraZeneca doses under review.

With less than two weeks remaining to fulfill President Biden’s pledge to share 80 million doses of coronavirus vaccine with countries in need, production problems at an Emergent BioSolutions manufacturing plant are forcing the administration to revise its plan to send AstraZeneca doses overseas.

Officials are now working to replace tens of millions of doses of the AstraZeneca vaccine that it had initially planned to include in the donation with others made by Pfizer and BioNTech, Moderna and Johnson & Johnson, according to people familiar with the discussions. Those three vaccines are authorized for emergency use in the United States; AstraZeneca’s is not.

A pattern of serious lapses at the plant, in Baltimore, has thrown into question the fate of more than 100 million doses of both the AstraZeneca and Johnson & Johnson vaccines made there. The Food and Drug Administration is poring over records of virtually every batch that Emergent produced to determine if the doses are safe. The F.D.A. has so far ruled that about 25 million Johnson & Johnson doses made at the factory can be released but has made no decision on the AstraZeneca doses.

AstraZeneca’s vaccine is significantly cheaper than the other three vaccines: The federal government paid less than $4 per dose, compared to as much as $19.50 for Pfizer. An administration official said that if the AstraZeneca doses made by Emergent are declared safe, the supply will ultimately be shared with other nations.

The doses the administration is now working to send overseas this month will be a part of existing orders from the other manufacturers that have not been delivered to states, one person familiar with the planning said. Tens of millions of doses of the three U.S.-authorized vaccines that have already been delivered to states are sitting unused. Over 175 million people in the U.S. have received at least one dose — more than 62 percent of the total population over 12 years old, according to the Centers for Disease Control and Prevention, and more than 148 million, or 52 percent, are fully vaccinated.

Until the White House announced last week that it would share 500 million doses of the Pfizer vaccine with the rest of the world, the AstraZeneca doses made up the bulk of the administration’s vaccine diplomacy commitments. ...