August 15, 2021 Analysis of USA state data
Summary: While most states continue to show rapid growth in cases (more that six weeks after the delta variant became dominant), there appears to be a reduction in transmission rate at the end of July. This may in part be due to the reversal in CDC mask mandates at that time.
Individual state histories
The plots below show the case / hospitalization / deaths data for all 50 states, DC, and PR. The data fits were done using data up until August 14, 2021.
The green points are the daily cases, the grey points the daily hospitalizations, and indigo points are the daily deaths (each averaged over a week). The case data are used to define the periods for which transmission rate appears to be constant. The vertical lines show where the transmission rate is changed. If the susceptibe fraction is constant (immunity not changing quickly), constant transmission rates lead to steady exponential growth or decline during, which appear as straight lines on these log-scale plots. With immunity growing, these lines are no longer straight - bending downwards due to the herd effect. The curves are the model expectations for cases, hospitalizations, and deaths, and all three are determined from the case data.
For this analysis, a long tail in the delay time between symptoms and hospital admission is included - which improves the model fits to hospitalization data. Now with this correction, the data appear to be consistent with the hypothesis that hospitalization probability is roughly constant (for most states).
The dashed curves separately show the reported cases from the original strains and from variants of concern, divided into two types B.1.1.7 (alpha) and B.1.617.2 (delta).
At the bottom of this page, plots showing the combined forecast for the US are shown.
District Of Columbia
The following plots show the combined US 4 week forecast. The shaded areas are 50%, 80%, and 95% intervals. Overall, cases are forecast to continue to grow, but at a rate that reduces over the coming weeks.