WASHINGTON, Dec 10 (Reuters) - The seven-day average of COVID-19 cases in the United States was up 37% and average deaths per day climbed 28%, Centers for Disease Control and Prevention Director Rochelle Walensky said on Friday. Initial data suggests that COVID-19 vaccine boosters help to bolster protection against the Omicron variant of the coronavirus, Walensky said at a White House briefing. Reporting by Ismail Shakil, Ahmed Aboulenein, and Jeff Mason Editing by Sonya Hepinstall