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FILE – In this April 26, 2021 file photo, a nursing student administers the Moderna COVID-19 vaccine at a vaccination center at UNLV, in Las Vegas. Biden’s plans to start delivering booster shots by Sept. 20 for most Americans who received the COVID-19 vaccines are facing new complications that could delay the availability of third doses for those who received the Moderna vaccine, administration officials said Friday, Sept. 3. (AP Photo/John Locher, File)