A bit late to the conversation here, but wanted to give my 2c - It's really going to depend on the MPH program; some are much more geared toward administration than policy, but you can work around this depending on what the specific school offers. If you know going in that policy is the direction you want to take, I think you can tailor your specific coursework toward that.
BUT, and this is where it gets dicey, you may actually do better getting a strong background in policy and economics (which was weirdly overlooked in quite a few of the programs I've seen) and picking up the public health as you go along.
*Disclaimer, I went through the UW Madison MPH program and felt it was very weak on economics, which can really undermine attempts to design policy.