A multi-center study to determine genetic variations in the fusion gene of respiratory syncytial virus (RSV) from children <2 years of age in the U.S.

The fusion (F) protein of respiratory syncytial virus (RSV) is the major target of immunoprophylactic monoclonal antibodies (mAbs) and vaccines. Recently reported mutations in F gene antigenic sites can vary among RSV types A and B. To further understand mutations in RSV F proteins, we performed subtyping and F gene sequencing on 400 RSV-positive respiratory samples collected at four pediatric hospitals within the United States from children under 2 years old between 2018 and 2020. RSV B was predominant in 2018-2019 and RSV A in 2019-2020 (55.5% and 85.5% respectively). Compared to the reference sequence, all RSV B samples had at least one antigenic polymorphism with the most changes at sites AM14/V (100%) and Ø (93.3%) followed by II (5.8%), IV (3.9%), and p27 (2.9%). The most frequent mutations among RSV B for AM14/V site were in L172Q (100%), S173L (100%), and K191R (95.2%) while for Ø site they were in I206M (93.3%) and Q209R (93.3%). Conversely, polymorphisms were observed in only 15.3% of RSV A samples overall, specifically at antigenic sites p27 (5.9%), IV (3.0%), II (2.5%), AM14/V (2.0%), I (2.0%), and Ø (0.5%). Among RSV A cases, T122A at p27 (n = 10) and S276N at II (n = 3) were the most common substitution sites. S276N at site II was found in both RSV types. Although polymorphisms in F proteins of RSV B were more common than those in RSV A samples, changes in both subtypes were observed in key F antigenic sites which could potentially impact the efficacy of mAb therapies and vaccines.