Fraction of all downsampled pre-capture reads that mapped to the reference genome (shown on the horizontal axis) for 24 viral genomes reflects a wide range of initial viral concentrations in these samples. Enrichment (shown on the vertical axis) was calculated by dividing the total number of post-capture reads mapping to a reference genome by the number of mapped pre-capture reads. Those with the highest viral content showed lower enrichment following capture with VALL. Seven of the 31 viral genomes included in the analysis are excluded from this plot because they yielded fewer than 200,000 total reads (Supplementary Table 3). Two IAV samples with a high fraction of viral reads pre-capture (bottom right) overlap on the plot. One sample (ZIKV-SM3, top left) showed no viral reads pre-capture, so its fold-change is undefined.