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The S&P 500 is shifting again. The index is adding two new components and dropping two to keep up to speed. Both Activision Blizzard Inc. (NASDAQ: ATVI) and United Continental Holdings Inc. (NYSE: UAL) are being added.

Activision Blizzard develops and publishes online, personal computer (PC), video game console, handheld, mobile and tablet games. United Continental provides air transportation services throughout the world. Headquartered in Chicago, the company will be added to the S&P 500 GICS Airlines Sub-Industry index.

Activision Blizzard will replace Pall Corp. (NYSE: PLL) after the close of trading on Friday, August 28. The reasoning behind this is that Danaher Corp. (NYSE: DHR) is acquiring Pall in a transaction expected to be completed on or about that date, pending final approvals.

Separately, United Continental will replace Hospira Inc. (NYSE: HSP) in the S&P 500 after the close of trading on Wednesday, September 2. Hospira is being acquired by Pfizer Inc. (NYSE: PFE) in a transaction expected to be completed on or near that date.

Shares of Activision Blizzard closed Thursday up 2.4%, at $27.93 in its 52-week trading range of $17.73 to $29.70. Following the announcement, shares were up 5.6% to $29.50 in early trading indications. The stock has a consensus analyst price target of $31.71.

United Continental closed Thursday down 1.1%, at $53.36 in its 52-week range of $39.46 to $74.52. In early trading indications shares were up 6.4% to $56.75. The consensus price target is $78.80.

Both stocks are taking a noticeable uptick, and rightfully so. Institutional buyers, in an effort to have their portfolios reflect the S&P 500 benchmark, will be loading up on these two stocks.

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