(Bloomberg) — U.S. stocks fell for a fourth day as investors assessed the prospects for a federal spending package and the likelihood for further virus-related economic restrictions.The S&P 500 Index turned lower in afternoon trading and is headed for its longest slide since September. The Nasdaq 100 Index advanced 0.9%, led by drugmakers after Alexion Pharmaceuticals Inc. agreed to be bought by AstraZeneca Plc. Energy producers tumbled with the price of crude after OPEC cut its demand forecast. The pound strengthened by the most in almost two months. The dollar extended its slump with Treasuries. Brazil’s Ibovespa Index erased losses for the year.Optimism from the start of Covid-19 shots gave way to concern over whether a relief bill from a bipartisan group of lawmakers would gain traction after its release later. The virus continued to rage in the U.S., threatening harsher restrictions across the nation. New York City Mayor Bill de Blasio warned that people should be prepared for a full shutdown and start making plans to work remotely.The Electoral College will officially elect Joe Biden president.“Signs of market fatigue are more prevalent today than a month ago, even as the popular average is near all-time highs,” wrote Paul Nolte, a portfolio manager at Kingsview Investment Management. “The much-awaited correction could come as investors tire of Washington, worry about the Covid cases over the holidays, or some other concern that is likely to pass in a few months rather than dominate the news cycle the way Covid has during the last nine.”The head of the U.S. government’s vaccination drive said as much as 80% of the population could be given the shot by next summer, putting “herd immunity” within reach. Wall Street strategists are in broad agreement that vaccines will supercharge the economy next year.“There is huge pent-up investment demand across the entire institutional world,” Michael Strobaek, global chief investment officer at Credit Suisse Group AG, told Bloomberg TV. “We’re steering into year-end with still tons of liquidity on the sidelines. I would not be on the wrong side of that.”Here are some key events coming up:Tuesday brings China industrial production and retail sales data for November.The Federal Reserve meets Tuesday and Wednesday, with markets widely expecting fresh guidance on its continued asset purchases.Policy decisions from the Bank of England and central banks in Mexico, Switzerland and Indonesia are due Thursday. Japan and Russia announce decisions Friday.These are the main moves in markets:For more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.©2020 Bloomberg L.P.