Investors saw record highs in the stock market on Monday, with the S&P 500, Nasdaq Composite, and Dow Jones Industrial Average all closing higher. Nvidia's post-stock split performance boosted tech stocks. Apple introduced "Apple Intelligence" at its Worldwide Developers Conference, focusing on personalization and privacy. Activist hedge fund Elliott Management revealed a $1.9 billion stake in Southwest Airlines and plans to replace the CEO and Chairman. Moderna's combination Covid-19 and flu vaccine showed promising results in late-stage trials, outperforming existing vaccines. CEO Stephane Bancel aims to file for U.S. approval this summer, with hopes of the vaccine hitting the market next year.