The United States will start to share up to 60 million doses of AstraZeneca Plc's COVID-19 vaccine doses with other countries as they become available, White House senior COVID-19 adviser Andy Slavitt said on Monday. 

"U.S. to release 60 million AstraZeneca doses to other countries as they become available," he wrote on Twitter. 

The Biden administration in March said it would send roughly 4 million of the drugmaker's vaccine to Canada and Mexico and is under growing pressure now to expand sharing of its stockpile with India and other countries.