  Vortex coronagraphs have been shown to be a promising avenue for
high-contrast imaging in the close-in environment of stars at thermal infrared
(IR) wavelengths. They are included in the baseline design of METIS. To ensure
good performance of these coronagraphs, a precise control of the centering of
the star image in real time is needed. We previously developed and validated
the quadrant analysis of coronagraphic images for tip-tilt sensing estimator
(QACITS) pointing estimator to address this issue. While this approach is not
wavelength-dependent in theory, it was never implemented for mid-IR
observations, which leads to specific challenges and limitations. Here, we
present the design of the mid-IR vortex coronagraph for the new Earths in the
$\alpha$ Cen Region (NEAR) experiment with the VLT/VISIR instrument and assess
the performance of the QACITS estimator for the centering control of the star
image onto the vortex coronagraph. We use simulated data and on-sky data
obtained with VLT/VISIR, which was recently upgraded for observations assisted
by adaptive optics in the context of the NEAR experiment. We demonstrate that
the QACITS-based correction loop is able to control the centering of the star
image onto the NEAR vortex coronagraph with a stability down to $0.015
\lambda/D$ rms over 4h in good conditions. These results show that QACITS is a
robust approach for precisely controlling in real time the centering of vortex
coronagraphs for mid-IR observations.
