First of all, VAS does not track the s&p 200. It follows the top...

First of all, VAS does not track the s&p 200. It follows the top 300. Secondly, the price will vary from the index some days due to an overly generous buyer or seller. I think it happens when the market makers are asleep at the wheel. The market markers don't recommend trading at open or close, due to the potential big variance like you noticed. It always corrects itself the very next day, when normal market conditions are in play. I hope this helps.

In other news, I think VAS is now back into the add zone.