Shares of cruise operators shot up on Monday toward their best gains in months, as some optimism from medical experts regarding the severity of the omicron variant assuaged investor fears over possible new COVID restrictions. Norwegian Cruise Line Holdings Ltd.'s stock /zigman2/quotes/204183397/composite NCLH -4.61% ran up 11.0%, enough to make it the biggest gainer among S&P 500 /zigman2/quotes/210599714/realtime SPX -1.89% components, and putting it on track for the biggest one-day gain Nov. 9, 2020, when it rocketed 26.8%. Elsewhere, Carnival Corp. shares /zigman2/quotes/202325446/composite CCL -3.89% were the S&P 500's third-best performers, hiking up 9.7% toward the best day since Nov. 16. And Royal Caribbean Corp.'s stock /zigman2/quotes/208854639/composite RCL -2.57% rallied 9.6%, and was the fourth biggest S&P 500 gainer; it was headed for the biggest gain since Feb. 16. The stocks' rallies come after they all closed at 13-month lows on Dec. 1. In comparison, the S&P 500 was rising 1.0%.