The short interest data are out for the November 28 settlement date. Biotech companies are considered a riskier group of stocks, with big upside and big downside. FDA rulings can make or break them. A single failed clinical trial can mean disaster for a stock. 24/7 Wall St. has reviewed the top biotech companies, without focusing on speculative companies, such as Ebola-vaccine companies.

The November 28 short interest data has been compared with the November 14 figures, and for the majority of the selected stocks, short interest is down.

Amgen Inc. (NASDAQ: AMGN) saw its short interest fall to 8.5 million shares, with 3.08 days to cover, from the previous level of 9.6 million. It would appear that this relative trend has been retreating from the 52-week short-interest high in September, and if this continues it could post its lowest short interest reading of the year. Amgen shares closed Tuesday down 1.3% at $169.39, in a 52-week trading range of $108.20 to $173.14.

Biogen Idec Inc. (NASDAQ: BIIB) saw its short interest remain relatively flat at 2.48 million shares, with 1.61 days to cover. The previous reading was 2.47 million with 2.01 days to cover. Investors seem to have grown optimistic on Biogen as this reading and the previous reading have indicated the lowest short interest of the year. Shares of Biogen Idec closed Tuesday up 1% at $347.61, in a 52-week trading range of $270.27 to $358.89.

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Celgene Corp. (NASDAQ: CELG) saw its short interest fall to 11.2 million shares, with 3.22 days to cover, compared to the previous reading of 12.4 million. It is worth noting that the current reading is the lowest short interest has been since the late March reading. Celgene shares closed Tuesday up about 0.4% at $118.68, in a 52-week trading range of $66.85 to $119.84.

Gilead Sciences Inc. (NASDAQ: GILD) saw its short interest increase to 56.6 million shares, with 3.49 days to cover. The previous reading for short interest was 53.9 million, with 3.41 days to cover. Including this reading, the previous five readings have been at the lower end of the short-interest range on the year. Gilead shares closed Tuesday up 0.3% at $105.90, in a 52-week trading range of $63.50 to $116.83.

Mannkind Corp. (NASDAQ: MNKD) saw its short interest fall to 79.7 million shares, with 22 days to cover. The previous reading was 82.4 million, with 17.24 days to cover. The current reading is the third highest of the year, just behind the previous two readings. Shares closed Tuesday down 0.3% at $5.47, in a 52-week trading range of $3.80 to $11.48.

Alexion Pharmaceuticals Inc. (NASDAQ: ALXN) saw its short interest fall to 2.65 million shares, with 3.52 days to cover. The previous reading was 2.8 million, with 3.34 days to cover. As investors seem to be growing more optimistic about Alexion, its current short interest continues to push lower lows on the year. Shares closed Tuesday up 1.3% at $199.77, in a 52-week trading range of $120.87 to $203.30.

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