Expert: ‘I've never seen a more rigorous chase for any vaccine’

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Jon Cohen, a staff writer for Science Magazine, tells Lawrence O'Donnell the race to develop a COVID-19 vaccine is "more rigorous" than any chase for a vaccine he has seen in his more than 30 years covering infectious diseases and vaccines. Cohen says he's hopeful because a COVID-19 vaccine does not seem "that tough of a scientific nut to crack.”