CNBC.com’s MacKenzie Sigalos brings you the day’s top business news headlines. On today’s show, CNBC’s Meg Tirrell runs through what we do and don’t know about Moderna’s 94% effective Covid-19 vaccine, and Pfizer’s 90% effective candidate. Plus, CNBC.com markets reporter Pippa Stevens breaks down Tesla’s addition to the S&P 500, and explains why the stock rallied today….