The Pfizer-BioNTech COVID-19 vaccine and the Moderna COVID-19 vaccine, both FDA-authorized for Emergency Use, require two shots. Individuals need to receive the same brand of vaccine for their second dose to be effective. The second shot of the Pfizer-BioNTech vaccine must be given three weeks after the initial dose. Moderna requires its second shot to be given one month after the original dose. The second dose should be received as close as possible to the 21 day/28 day time, but does not have to be on the precise day and can be administered later without repeating the series. The Johnson & Johnson vaccine only requires one dose. People are encouraged to take whatever vaccine is being offered to them rather than wait for a specific brand.