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In the FRG framework a sufficient condition for scale invariance to imply conformal invariance is that there is no integrated vector operator symmetric under all internal symmetries (of the considered model) and having scaling dimension exactly −1. We compute the scaling dimensions of vector operators in the O(N)-model in various approximations (ε-expansion, large N limit and at o(∂^3) in the Derivative Expansion of the Non-Perturbative Renormalization Group). We find that the scaling dimensions of all considered integrated vector operators are always much larger than −1 for any N. Moreover, we extended the existing proof of the inequality in the Ising universality class to the O(N) case with N ∈ {2,3,4}.