You have a design decision to make: if your content is meant to scroll horizontally, then a user swipe over a switch is ambiguous -- does it mean they want to scroll, or toggle the switch?
The easiest solution is to modify your UI so that this ambiguity disappears. For example, if the scroll's contentSize is not wider than the bounds of the scroll view, then it can't scroll horizontally, and a horizontal swipe will always activate the switch.
If you do want to allow horizontal scrolling, then it makes sense to replace the UISwitch with a UIButton that toggles on touch, similar to a play/pause button.
On the other hand, if you don't want to modify your UI, you could always just do:
myScrollView.delaysContentTouches = NO;
This will cause your switch to "get" the touches immediately, rather than have them go to the UIScrollView first. More info here. (You can also set this boolean in Interface Builder, as pointed out by Squeegy.)