  We establish a quantitative isoperimetric inequality for weighted Riemannian
manifolds with $\mathrm{Ric}_{\infty} \ge 1$. Precisely, we give an upper bound
of the volume of the symmetric difference between a Borel set and a sub-level
(or super-level) set of the associated guiding function (arising from the
needle decomposition), in terms of the deficit in Bakry-Ledoux's Gaussian
isoperimetric inequality. This is the first quantitative isoperimetric
inequality on noncompact spaces besides Euclidean and Gaussian spaces. Our
argument makes use of Klartag's needle decomposition (also called
localization), and is inspired by a recent work of Cavalletti, Maggi and
Mondino on compact spaces. Besides the quantitative isoperimetry, a reverse
Poincar\'e inequality for the guiding function that we have as a key step, as
well as the way we use it, are of independent interest.
