Since you have tagged this with “American Government,” I will assume that you are asking about inoculation advertising in the political context.
Inoculation advertising is meant to introduce a consumer (or, in this case, a voter) to the ideas of the advertiser’s rival. In the political sphere, this would take the form of a something like a candidate having an ad that starts out by giving her opponent’s main selling points. The ad would then go one to tear that selling point down. The point of this is to give the voter a sample of what the opponent has to say so they will be more resistant to that message when they hear it.
The likely effect of this sort of advertising is to make voters skeptical of both candidates since they are likely to be exposed to inoculation ads on both sides. Voters will be told that they should not believe either candidate’s main sales pitch. This is likely to turn voters off of both candidates. Such advertising will likely lead to greater cynicism and less inclination to vote.