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The Moderna COVID-19 (mRNA-1273) vaccine: what you need to know
Biden to ban travel from South Africa, reinstate restrictions on Brazil and U.K.
By Stephanie Beasley
EXPLAINER: Why it's hard to make vaccines and boost supplies
By Lauran Neergaard
First Moderna, now Pfizer-BioNTech working on booster shot amid rise of COVID-19 variants
By Angus Liu
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How scientists can 'copy and paste' Covid vaccines to work on the strain from South Africa
By Cory Stieg
Biden to impose travel restrictions on South Africa, U.K. and Brazil to mitigate new Covid strains
By Leslie Josephs & Emma Newburger