Recently, with Galactic Cosmic Ray (GCR) observations available from the state-of-the-art space experiments (AMS-02, PAMELA, et.al.), the solar modulation of these particles has been studied on different time scales over a wide rigidity range. A clear 27-day-periodicity is confirmed in the fluxes of protons and revealed for GCR helium. It is well known that Corotating Interaction Regions (CIRs) are the main driver for this periodicity. In this study, using a hybrid MHD-GCR transport numerical model, we investigate CIR effects on helium and proton fluxes close to the Earth. It was found that: Protons and the two helium isotopes are modulated differently by a CIR; as expected the magnitude of this decrease varies with GCR rigidity.