Superconformal field theory (SCFT) with N=2 supersymmetry in four dimensional spacetime provides a prime playground to study strongly coupled phenomena in quantum field theory. Recently, Rastelli et.al has constructed a remarkable map from 4d N=2 SCFTs to 2d chiral algebras (VOAs) such that the vacuum character of the corresponding VOA reproduces the limit of the superconformal index, called the Schur index. In this talk, I will discuss the representations of some simple affine vertex algebras at non-admissible level arising from rank one 4d N=2 SCFTs. This talk is based on joint work arxiv:2403.04472 with Tomoyuki Arakawa, Xuanzhong Dai, Justine Fasquel and Anne Moreau.