in vitro transcription of a plasmid-derived A/Cal07 HA segment using T7 RNA polymerase, which then was used as a template for RT-PCR to produce the amplicon library for sequencing. (Fig5)
We used the universal amplification, pioneered by Zhou et al., to generate 8-segment, full-length amplicons from viral samples and sequence them using the Illumina MiSeq platform. See the paper for more info