Wall Street’s main indexes rose for a third straight session on Thursday after early data suggested the Omicron variant of the coronavirus was less severe than feared, lifting the mood ahead of Christmas break. The S&P 500 was within striking distance of its record high hit on Nov. 22, riding on broader gains, including in travel-related stocks, which are highly sensitive to pandemic-related news. Casino operators Melco Resorts & Entertainment Ltd, Wynn Resorts, and MGM Resorts rose between 1 percent and 6 percent, while the S&P 1500 airlines index advanced 0.7 percent. Two vaccine makers said their shots offered protection against Omicron, as UK data suggested it may cause proportionally fewer hospitalizations than the Delta coronavirus variant, supporting conclusions reached in South Africa. World Health Organization officials have, however, warned against drawing firm conclusions about its virulence. As investors head into the new year following what has been a bumper …