A COVID-19 vaccine candidate developed by the U.S. company Moderna and the National Institutes of Health starts its final phase of testing. It's one of a handful of candidates to reach this stage.
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Joe Palca is a science correspondent for NPR. Since joining NPR in 1992, Palca has covered a range of science topics — everything from biomedical research to astronomy. He is currently focused on the eponymous series, "Joe's Big Idea." Stories in the series explore the minds and motivations of scientists and inventors. Palca is also the founder of NPR Scicommers – A science communication collective.