(For a Reuters live blog on U.S., UK and European stock markets, click LIVE/ or type LIVE/ in a news window) * Alibaba sinks on Chinese regulatory ire * Amazon leads gains in consumer discretionary * Alexion Pharma among top boosts on AstraZeneca offer * Indexes: Dow +0.04%, S&P 500 +0.20%, Nasdaq +0.96% (Updates with afternoon trading) Dec 14 (Reuters) - The S&P 500 rose on Monday after the launch of a nationwide COVID-19 vaccine campaign in the United States, while Alexion Pharmaceuticals jumped on a $39 billion buyout offer from AstraZeneca in one of the year’s biggest deals. Administration of the vaccine developed by Pfizer and its German partner BioNTech began on Monday following emergency-use approval from federal regulators last week. The S&P 500 consumer discretionary index led gains among sector indexes, with Amazon rising 2%. The S&P 500 gave up most of its gains after rising almost 1%. The index has surged 14% to record highs in 2020, despite the pandemic, which has wrought economic devastation and killed more than a million people. “While the entire market is pleased, is optimistic, is bullish about the arrival of the vaccine this morning into the U.S., I think the average investor is realizing that this roll-out, this distribution of the vaccine is not going to be a silver bullet, is not going to go as fast as one hopes,” said Jake Dollarhide, chief executive officer of Longbow Asset Management in Tulsa, Oklahoma. Alexion Pharmaceuticals Inc was among the top boosts to the S&P 500 and the Nasdaq, surging about 30% to a 4-1/2 year high after British drugmaker AstraZeneca said it would buy the U.S. biotech firm. AstraZeneca’s U.S.-listed shares fell more than 7%. The Dow Jones Industrial Average was up 0.04% at 30,059.53 points, while the S&P 500 gained 0.20% to 3,670.83. The Nasdaq Composite added 0.96% to 12,496.99. Uncertainty over more fiscal stimulus cut short a rally in U.S. stocks after the Senate last week approved a one-week extension of federal funding to avoid a government shutdown and allow more time for negotiations on coronavirus relief and an overarching spending bill. The focus was also on early voting in a pair of U.S. Senate races in Georgia that will determine control of the chamber and heavily influence lawmaking. E-commerce company Alibaba Group Holding Ltd shed almost 3% after China warned its internet majors of more anti-trust scrutiny, imposed fines and announced probes into deals involving Alibaba and Tencent Holdings Ltd. Electric-car maker Tesla Inc rose 4% as anticipation of its addition to the S&P 500 benchmark next week offset a report of production delays. Walt Disney Co fell about 2.5% after rallying on Friday and was the biggest drag on the Dow after BMO Capital Markets downgraded the stock. Advancing issues outnumbered declining ones on the NYSE by a 1.05-to-1 ratio; on Nasdaq, a 1.29-to-1 ratio favored advancers. The S&P 500 posted 25 new 52-week highs and no new lows; the Nasdaq Composite recorded 205 new highs and 12 new lows. (Additional reporting by Ambar Warrick and Shreyashi Sanyal in Bengaluru; editing by Barbara Lewis)