Jan 15 (Reuters) - Pfizer Inc has been holding onto second doses for each of its COVID-19 vaccinations and anticipates no problems supplying them to Americans, a spokeswoman said in a statement on Friday.

Pfizer has shipped more than 15 million doses to destinations around the U.S. from its Michigan facility and expects to be able to produce around 2 billion doses worldwide in 2021, the spokeswoman said, adding that U.S. health officials recently asked the company to begin distributing its second doses.

(Reporting by Carl O'Donnell; Editing by Leslie Adler)