- Worst-hit nation -The United States on Friday authorised Moderna's Covid-19 vaccine for emergency use, paving the way for millions of doses of a second jab to be shipped across the hardest-hit country in the world.The United States is the first nation to authorise the two-dose regimen from Moderna, now the second vaccine to be deployed in a Western country after the one developed by Pfizer and BioNTech.Millions of doses will start shipping out as early as this weekend from cold-storage sites outside Memphis and Louisville.With the United States now registering more than 2,500 deaths a day from Covid-19, senior US officials including Vice President Mike Pence stepped up to receive early vaccinations on Friday.Pence's public inoculation was.