U.S. stocks were mostly lower at the start of Friday’s session as markets struggled to extend their record-setting rally, with analysts citing a lack of new catalysts for further gains. The S&P 500 fell 0.1% to 3,912. The Nasdaq Composite slid 0.4% to 13,963. The Dow Jones Industrial Average advanced 0.1% to 31,463. President Joe Biden on Thursday said the U.S. would have enough COVID-19 vaccines by the end of the summer to inoculate 300 million Americans, but suggested it may take time to get those vaccines into arms. Shares of Walt Disney Co. rose 1.7% after the entertainment company delivered a surprise fourth-quarter profit.