In a generally positive first half of the year, the biggest winner so far among S&P 500 stocks was Vertex Pharmaceuticals, up a whopping 74.9 percent. Its shares jumped 21 percent in a single day back in March when the company revealed two of its cystic fibrosis drug trials yielded positive results, helping it become the top-performing stock in the entire S&P 500 in the first half of the year.
The rest of the top five:
2. Activision Blizzard, up 59.4 percent
3. Align Technology, up 56.1 percent
4. Wynn Resorts, up 55.0 percent
5. CSX Corporation, up 51.8 percent