title: Illumina MiSeq paired end sequencing
library_construction_protocol: Viral RNA was extracted using QIAamp Viral RNA Mini Kit (Qiagen). Reverse transcription was performed using SuperScript III First-Strand Synthesis System for RT-PCR (Thermo Fisher Scientific). cDNA was used to amplify fragments containing env mutation using Q5 High-Fidelity DNA Polymerase (New England Biolabs).