The US just authorized a 3rd coronavirus shot, adding a convenient, single-dose option to boost the rollout

Johnson & Johnson's coronavirus vaccine is delivered as a single shot, while both Pfizer and Moderna's require two jabs.
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The FDA just authorized Johnson & Johnson's single-dose coronavirus vaccine.
The decision comes after a panel of independent experts voted unanimously on Friday in favor of recommending the shot. 
J&J has said it will be ship nearly 4 million doses immediately following a regulatory OK. 
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