US regulators approved a second Covid-19 vaccine in a single week's time, greenlighting a shot developed by Moderna Inc. and the National Institutes of Health for emergency use for Americans 18 years and older.

The Moderna approval comes exactly a week after the US Food and Drug Administration okayed a shot from Pfizer and its German partner BioNTech. Moderna expects to have 85-100 million shots available in the US in the first three months of 2021. Vaccinations are set to begin Monday.