TAOYUAN, Taiwan—Taiwan welcomed 2.5 million COVID-19 vaccine doses from the United States on Sunday as help from a true friend, more than doubling the major semiconductor-producing island’s arsenal of shots as it deals with a cluster of domestic infections. Washington, competing with Beijing to deepen geopolitical clout through “vaccine diplomacy,” initially had promised to donate 750,000 doses but increased that number as President Joe Biden’s administration advances its pledge to send 80 million U.S.-made shots around the world. A China Airlines Boeing 777 freighter carrying the vaccines landed at Taoyuan airport outside of Taipei late afternoon, greeted on the tarmac by Health Minister Chen Shih-chung and the top U.S. diplomat in Taiwan, Brent Christensen. Speaking from her office in comments broadcast after the arrival of the Moderna shots, President Tsai Ing-wen expressed her “sincere gratitude.” “A friend in need is a friend indeed,” she added, switching into English. The American …