WASHINGTON, Dec 21 (Reuters) - U.S. health authorities are considering reducing the 10-day recommended quarantine period for Americans who test positive for COVID-19 as the Omicron variant tears across the country, White House medical adviser Anthony Fauci said on Tuesday. A spike in COVID-19 cases is alarming public health officials, who fear an explosion of infections following social mingling over the Christmas and New Year holidays. Omicron now accounts for 73% of U.S. coronavirus infections, the federal Centers for Disease Control and Prevention (CDC) said Monday. read more Breakthrough infections are rising among the fully vaccinated population, including those who have had a third, booster shot. However, Omicron appears to be causing milder symptoms in those people, some of whom have no symptoms at all. Reducing the CDC"s 10-day quarantine recommendation would help asymptomatic people return to work or school, with the proper precautions, Fauci told CNN. "That"s certainly an important consideration which is being discussed right now," said Fauci, director of the National Institute of Allergy and Infectious Diseases. Delta Air Lines (DAL.N) Chief Executive Ed Bastian on Tuesday asked CDC Director Rochelle Walensky to shrink quarantine guidelines for fully vaccinated individuals who experience breakthrough COVID-19 infections to five days. "With the rapid spread of the Omicron variant, the 10-day isolation for those who are fully vaccinated may significantly impact our workforce and operations," Bastian wroteTuesday in a letter with airline medical advisors. The CDC declined comment. Delta"s letter added that "similar to healthcare, police, fire, and public transportation workforces, the Omicron surge may exacerbate shortages and create significant disruptions." Bastian said "individuals would be able to end isolation" with testing after five days of isolation. The measure is being considered particularly in the context of healthcare workers, as the number of COVID cases rises along with the need for healthcare personnel, Fauci said. With Omicron being so easily transmissible, the number to watch in this surge is hospitalizations, not overall infections. "If you really want to look at the true impact on society, it"s much more important to see who gets sick and who doesn"t, who requires hospitalization, or doesn"t," Fauci said.