ITER disruptions will typically involve a vertical motion of the plasma. As the plasma touches the upper or lower wall, part of the plasma current will be transferred into halo current. A substantial fraction of the initial plasma current may remain as halo current by the time all flux surfaces (FS) are open. In the halo region, electrons cannot run away since they would promptly hit the wall. Considering that the runaway electron (RE) avalanche gain is related to the change in plasma current, it may thus be naively expected that this gain is significantly reduced by the plasma vertical motion. We investigated this question by simulating disruptions with vertical plasma motion in ITER using an axisymmetric 2D model in the JOREK-STARWALL code. The disruption begins with a thermal quench (TQ) triggered by an artificial increase of the heat conductivity. An impurity injection is then performed so that the energy is further dissipated via radiation. To simplify the simulation, the impurity is from a constant source instead of realistic injections. During the ensuing current quench (CQ), the vertical motion of the plasma and the halo current are self-consistently simulated. In these preliminary simulations, REs are not included in the model. However, we estimated the potential RE avalanche gain on each FS (labelled by its toroidal flux $\phi_t$) by calculating the change in the poloidal magnetic flux $\Delta\psi_p$ on that surface between the start of the simulation and the time when the surface becomes open due to the vertical motion. The potential avalanche gain should be exponentially sensitive to $\Delta\psi_p$ [1]. The simulations with vertical motion show smaller $\Delta \psi_p$ compared to those with a stationary plasma but, rather disappointingly, the difference is modest. We will discuss this result and propose an interpretation. Besides the RE avalanche gain, these simulations allow investigating other interesting aspects related to the vertical plasma motion during an ITER disruption, which we will also discuss. [1] Allen H. Boozer. Theory of runaway electrons in ITER: Equations, important parameters, and implications for mitigation. Physics of Plasmas, 22(3), 03 2015. 032504.