By Herbert Lash and Julien Ponthus NEW YORK/LONDON, Dec 6 (Reuters) - U.S. and European shares rallied on Monday and the dollar edged higher after reassuring news on the Omicron COVID-19 variant bolstered investor sentiment. The rebound after a recent sell-off shows investors are not giving up on the prospect of a Santa Claus rally, said Sam Stovall, chief investment strategist at CFRA Research. "By severely limiting the FOMC's ability to respond to downside risks posed by Omicron, inflation has effectively destroyed the Fed put," Jefferies analysts said in note.