One interesting effect might be an 'arms race' between illicit drug producers and vaccine makers. As children become 'vaccinated' against the common drugs of abuse, the market for street drugs would fragment and diversify into drugs that don't have vaccines yet.
I can think of other equally dystopian scenarios. How about government-sanctioned vaccinations against creativity for grade-schoolers? (Tell parents their children will be better-behaved and they'll almost certainly comply, at least in the U.S. Because, after all, it's such a seductive trade-off.)