By Ben Blanchard TAIPEI, June 6 (Reuters) - The United States will donate 750,000 COVID-19 vaccine doses to Taiwan as part of the country's plan to share shots globally, U.S. Senator Tammy Duckworth said on Sunday, offering a much-needed boost to the island's fight against the pandemic. Taiwan is dealing with a spike in domestic cases but has been affected like many places by global vaccines shortages. Only around 3% of its 23.5 million people have been vaccinated, with most getting only the first shot of two needed. Speaking at Taipei's downtown Songshan airport after arriving on a three-hour visit with fellow Senators Dan Sullivan and Christopher Coons, Duckworth said Taiwan would be getting 750,000 doses as part of the first tranche of U.S. donations.