The United States hit a record 16 million Covid-19 cases on Saturday afternoon, with deaths closing in on the 300,000 mark, even as millions of doses of a new vaccine were expected to start rolling out across the nation on Sunday.

The first vaccine was approved late on Friday by the US Food and Drug Administration and is expected to touch off a mass-inoculation campaign of unparalleled dimension to end the pandemic that has upended daily life and devastated the US economy...