To fight the pandemic at home, the United States gave its own vaccine manufacturers priority access to American-made materials needed to make the shots. As a result, the U.S. government laid claim not only to vast quantities of finished COVID-19 vaccines but also to vaccine components and equipment all along the supply chain, according to a Reuters review of more than a dozen contracts involving some major suppliers. That has left some countries desperately in need of those supplies to scramble for substitutes, exacerbating international disparities in vaccine access, according to interviews with suppliers, foreign manufacturers and vaccine market experts. On Wednesday, President Joe Biden threw his support behind waiving patents for COVID-19 vaccines, thrilling those who have been pressuring his administration to help speed production of doses worldwide. If adopted by the World Trade Organization, the move would let other countries make their own copies of the much-coveted shots.