You don't need to, but it certainly wont hurt it at all.
Infact, I'd suggest that you do because it's preferable to start with the cleanest surface you can if you're going to be putting synthetic sealants like Zaino on the car, which can last 6 months or more.
I'd be inclined to clay the whole car so you've removed absolutely everything from the paint before sealing it with Z.
Despite the fact it's only a few weeks old, that doesn't mean there aren't tiny particles of crud already on your paint.
Go for it... :thumbsup: You'll only end up with a more perfect blank canvas to apply Z onto...