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The Moderna COVID-19 (mRNA-1273) vaccine: what you need to know
Biden to impose travel restrictions on South Africa, U.K. and Brazil to mitigate new Covid strains
By Leslie Josephs & Emma Newburger
EXPLAINER: Why it's hard to make vaccines and boost supplies
By Lauran Neergaard
Pfizer working on booster shot to protect against COVID-19 variants
By Dania Nadeem