On my Thinkorswim.com option trading screen, the possible vertical spreads for KERX are 10/12.5, 12.5/15. That suggests to me that the market doesn't expect many 5 point spreads for a stock at this price.
A bigger question, why would you buy such expensive options? The historical volatility is only 66% and the implied volatility on options for all three strikes is about 150%. This means all of the options prices could fall sharply even if the stock's price doesn't change. That would make the trade a quick and sure loser.
The logic, of course, is that you are expecting the price of the stock to move to $12.5 or so from about $10. This would give you a 2.5 loss on the 15 strike and a 2.5 gain on the 10 strike. To make money, you'd need to see the stock rise to at least $13, giving you a 50 cent profit. See M*'s math in the previous post.
For me, this suggested trade is a great case history of what makes a good vertical spread. You're expecting a news event that will cause the stock to rise. You limit your risk by buying a 10 strike and selling a 15 strike. As the trade nears the March 21 maturity, assuming the stock holds at $10, the price of the 15 will fall, giving you a profit. If the stock falls to $9 or $8, prices on both options will drop, and you'll probably lose money, because the higher-priced 10 call will lose more than the shorted (written, sold) lower priced 15 calls will make. You have to watch the trade like a hawk, by the minute or hour, not by the week or month.
M* is assuming that if the stock rises to $20, you'll call the stock and pay $10 for it and hold it, making this a long-term investment.
Most traders, however, would take their profit on the spread and move on rather than put up the money to buy the stock. If you're sophisticated enough to do this trade, wouldn't you be sophisticated enough to continue to leverage your cash doing spreads rather than use your money to buy a stock?
I wonder why M* doesn't call this a "vertical spread," which is what it is?