Wall Street’s main indexes rose solidly for a third straight session on Thursday after more encouraging developments about the impact of the Omicron variant of the coronavirus, lifting the mood ahead of Christmas break. The S&P 500 was near its intraday record high as most sectors gained. Industrials and consumer discretionary were the top-performing sectors, both up about 1.3 percent. Vaccine makers AstraZeneca Plc and Novavax Inc said their shots protected against Omicron as UK data suggested it may cause proportionally fewer hospital cases than the Delta variant, though public health experts warned the battle against COVID-19 was far from over. The arrival of Omicron has helped ratchet up market volatility for much of the last month of 2021, which has been a strong year for equities. “There was a lot of negative sentiment coming into the final part of the year, and investors have likely continued to see pretty …