NEW DELHI (AP) — The chief executive of Serum Institute of India, the world’s largest maker of vaccines and a critical supplier of the U.N.-backed COVAX facility, has asked President Joe Biden on Twitter to lift the U.S. embargo on exporting raw materials needed to make the the jabs. Vaccine makers and experts in India have been concerned that the use of the Defense Production Act by the U.S. to boost their own vaccine production was resulting in exports of critical raw materials being stopped. This was hobbling vaccine production in other parts of the world. Serum Institute of India has paused exports to COVAX after a devastating surge of infections in India resulted in increased domestic demand.