S&P 500 top movers: Alexion Pharmaceuticals Inc (ALXN: NASDAQ) up more than 30%

• S&P 500 lost its traction after starting the day decisively higher.
• Alexion Pharmaceuticals Inc (ALXN: NASDAQ) post impressive gains on Monday.
• Energy stocks suffer heavy losses at the start of the week.

The S&P 500 Index (SPX) opened sharply higher and gained nearly 1% in the first hour of the session on Monday. However, the negative shift witnessed in risk sentiment weighed on major equity indexes and the SPX was last seen gaining only 0.1% on the day at 3,667.

S&P 500 top movers

Over the weekend, AstraZeneca PLC (AZN: NASDAQ) announced that it will acquire US-based biotech company Alexion Pharmaceuticals Inc (ALXN: NASDAQ) for about $39 billion. This development caused AZN to suffer heavy losses and provided a strong boost to ALXN. As of writing, ALXN was the biggest daily percentage gainer of the day, rising 30.5% to trade at its highest level in more than four years at $157.96. 

Incyte Corp (INCY: NASDAQ), Mosaic Co (MOS: NYSE) and ABIOMED Inc (ABMD: NASDAQ) shares are among the other top performers on Monday, up between 4.5% and 7.2%.

On the other hand, major energy stocks are falling sharply on Monday. Earlier in the day, OPEC in its monthly report revised its forecast for 2021 global energy demand recovery lower due to coronavirus uncertainty and mild winter expectations. At the moment, Occidental Petroleum Corp (OXY: NYSE), Diamondback Energy Inc (FANG: NASDAQ) and Marathon Petroleum Corp (MPC: NYSE) stocks are losing between 6.8% and 3.7%.