The United States on Wednesday promised to buy 500 million more COVID-19 vaccine doses to donate to other countries as it comes under increasing pressure to share its supply with the rest of the world. br br Under increasing pressure to share America’s COVID-19 vaccine supply with other nations, U.S. President Joe Biden on Wednesday promised to donate an additional 500 million PfizerBioNTech shots to poorer countries around the world.br br That brings the U.S.’s total global commitment to 1.1 billion vaccines so far – more than any other nation.