Replication of the negative sense genomic RNA of the human respiratory syncytial virus (RSV) occurs through the positive sense intermediate, also known as antigenomic RNA. RNA synthesis is performed by the RNA-dependent RNA polymerase (RdRP) complex composed at a minimum of the L protein, which is the catalytic subunit of RdRP, and P protein. Protein M2-1 that acts as a processivity factor is described as a consitutive RdRP subunit by some and as an accessory RdRP subunit by other studies (reviewed in Fearns and Deval 2016). Replication of both genomic and antigenomic RNA depends on encapsidation by protein N, which has regions that interact with both protein P and protein L. Encapsidation protects genomic and antigenomic RNA from degradation as these RNAs do not possess the 5' cap and the poly(A) tail. Replication occurs after primary transcription. Accumulation of the protein M2-2 is responsible for the shift of RNA synthesis from transcription to replication through a mechanism that has not been fully elucidated (For review, refer to Collins and Melero 2011, Battles and McLellan 2019).