WASHINGTON – Hundreds more U.S. hospitals will begin vaccinating their workers Tuesday as federal health officials review a second COVID-19 shot needed to boost the nation’s largest vaccination campaign.Packed in dry ice to stay at ultra-frozen temperatures, shipments of Pfizer’s COVID-19 vaccine are set to arrive at 400 additional hospitals and other distribution sites, one day after the nation’s death toll surpassed a staggering 300,000.