Fig. 4. The estimated effect of Alpha and Delta variant on SARS-CoV-2 (N1) wastewater concentration normalized by pepper mild mottle virus in sewersheds of Jefferson County, KY (USA).

The dark brown line is the regression-based fit to the wastewater concentration with the Alpha and Delta variant and the light brown line is the prediction of wastewater concentration using synthetic prevalence from the $SV{I}_{2}RT$ model with the Alpha variant only. The shaded areas represent 95% credible intervals. The blue dots are observed weekly average wastewater concentration. The panels compare the variant effect on wastewater concentration for Jefferson County (a) as well as stratified by sewershed (b–d).