[zaroth]

25% prevalence is absolutely not in line with what experts were saying on March 23rd. Nor was an IFR of 0.5%.

The CDC reports that flu has an IFR of ~.13% in the US (61,000 deaths out of 45 million cases). That makes 0.5% roughly 3.3 times worse, not 10.

Also, herd immunity does not require 100% having positive antibodies, it will show an effect on Ro starting around 65%.

[nodamage]

Bear in mind that the CDC estimate of 45 million influenza cases[1] is the number of symptomatic cases, and therefore it doesn't really make sense to directly compare that with Covid-19 IFR rates calculated from antibody studies which include both symptomatic and asymptomatic cases.

[1] https://www.cdc.gov/flu/about/burden/2017-2018.htm

[hcknwscommenter]

It's not 25%. 0.5% versus 0.13% is not the only issue here in terms of how much worse it is. It's the long time in the ICU. The flu kills you fairly quickly or you get better fairly quickly, so you don't take up hospital capacity so long. Herd "immunity" does not require 100%, but that's a decent approximation. Sure, I'll grant that it "starts" to show an effect around 65%, but the effect is not so strong. 70%, much stronger. 80% very strong. Heck, you could probably do containment by then without waiting to get to 100%. Because inadvertent spreading would be so low.

[bagacrap]

it would show an effect on r0 immediately, but around 65 is when r0 would hit 1 (since it's got 2/3 fewer chances to spread and starts at about 3)