We have to ask why smallpox was a unique event, and we never used this method for any other virus. Did we even ever consider it?
There are two strains of smallpox, one of which is much less deadly than the other. People practicing variolation tended to use variolous material from a mild cases, including those successfully variolated. Some of the success of smallpox variolation was probably due to this practice and the resulting tendency for the inoculations to contain variola minor.
The model seems not far off estimating peak hospitalization date, at least for states that are currently peaking like CA and NY. The peaks in places that are close to peaking can be pretty accurately estimated just with curve fitting though, I assume that being fit to past data is why the model works OK for this.
It’s clearly overly optimistic about the rate of drop-off after the peak in deaths, at least in some cases. Look at Spain and Italy. Right now here’s how they look:
Italy: graph shows 610 deaths on April 9. Predicts 335 on April 10, 281 on April 11. Actual is 570 on April 10, 619 on April 11.
Spain: graph shows 683 on April 8, Predicts 372, 304, 262 on next three days. Actual 655, 634, 525.
The model for New York says deaths will be down to 48, 6% of the peak, in 15 days. Italy is 15 days from it’s peak of 919 and is only down to 619, 67% of the peak.
The model for the US as a whole is a little less obviously over-optimistic, assuming the peak really was April 10. it’s only predicting 40% decline in the next 15 days. California model predicts an even slower decline. It seems to think fast growth in cases in the outbreak phase leads to fast recovery, which has not been borne out thus far in Italy and Spain.