U.S. stock indexes struggled for direction on Wednesday after a strong start to the week, as investors digested a fresh update on Pfizer and BioNTech’s COVID-19 vaccine, while the fast-spreading Omicron variant kept bigger bets in check. Pfizer and BioNTech said their three-shot course of COVID-19 vaccine was able to neutralize the new Omicron variant in a laboratory test and they could deliver an upgraded vaccine in March 2022 if needed. Travel stocks rebounded, with the S&P 1500 Airlines index up 3.7 percent, while Norwegian Cruise Line led gains among cruiseliners. Markets were cautious after reports earlier in the day said Britain could implement tougher COVID-19 measures, including advice to work from home, as early as Thursday in a bid to slow the spread of the Omicron variant. Six of the 11 major S&P 500 sector indexes rose. Financials and utilities led to declines. Technology-oriented growth stocks, which have been …