Great question. We don't have exact numbers in humans like we do in mice, because we don't have randomized controlled trials, so there are lots of other factors that change at the same time that variants change- for example, hospital capacity, treatments, selection effects of who is infected. Also, there is a lot less research on the Washington strain than on Delta, but they are much closer related to each other than to Omicron, and there was not a noticeable difference between the two in terms of pathogenicity. This twitter thread breaks down what we do know, with great graphs: https://twitter.com/jburnmurdoch/status/1488084567760244736
When comparing unvaccinated 70 yr olds, the risk of ICU admission was 3.5 times higher for Delta than for Omicron. Delta was more transmissible than Omicron, but about as pathogenic as the Washington strain. Also, the infection fatality rate in January 2020 was over 20x that of the flu, while during the Omicron wave in January it was only about 2x as deadly as the flu in the UK. Even comparing from late 2021 to early 2022 there was around a 3x drop in the case fatality rate in the US.
TL;DR- at least 3 times as deadly as Omicron, possibly more.
How dangerous was the Washington strain to humans?
Great question. We don't have exact numbers in humans like we do in mice, because we don't have randomized controlled trials, so there are lots of other factors that change at the same time that variants change- for example, hospital capacity, treatments, selection effects of who is infected. Also, there is a lot less research on the Washington strain than on Delta, but they are much closer related to each other than to Omicron, and there was not a noticeable difference between the two in terms of pathogenicity. This twitter thread breaks down what we do know, with great graphs: https://twitter.com/jburnmurdoch/status/1488084567760244736
When comparing unvaccinated 70 yr olds, the risk of ICU admission was 3.5 times higher for Delta than for Omicron. Delta was more transmissible than Omicron, but about as pathogenic as the Washington strain. Also, the infection fatality rate in January 2020 was over 20x that of the flu, while during the Omicron wave in January it was only about 2x as deadly as the flu in the UK. Even comparing from late 2021 to early 2022 there was around a 3x drop in the case fatality rate in the US.
TL;DR- at least 3 times as deadly as Omicron, possibly more.