  Chiral de Rham complex introduced by Malikov et al. in 1998, is a sheaf of
vertex algebras on any complex analytic manifold or non-singular algebraic
variety. Starting from the vertex algebra of global sections of chiral de Rham
complex on the upper half plane, we consider the subspace of $\Gamma$-invariant
sections that are meromorphic at the cusps. The space is again a vertex
operator algebra, with a linear basis consisting of lifting formulas of
meromorphic modular forms. We will describe two types of lifting formulas, and
generalize the Rankin-Cohen bracket to the meromorphic modular forms. As an
application, we will show that the vertex algebras constructed by congruence
subgroups are simple.
