HotardAg07 said:
While I do think that 20% infection rate PLUS other mitigation measures (whether government enforced or not) may be enough to have sustained R_t < 1, it is worth noting that there ARE areas that had >20% infection rate.
In Bergamo, Italy -- one of the first hot spots that was late to shut down after experiencing their outbreak, had 57% of their residents get coronavirus.
https://www.reuters.com/article/us-health-coronavirus-italy-antibodies/over-half-of-people-tested-in-italys-bergamo-have-covid-19-antibodies-idUSKBN23F2JV
https://www.medrxiv.org/content/10.1101/2020.04.15.20067074v3
The death rate of the entire population was 0.58%, which means that if 57% of the entire population was infected, then the infection fatality rate is about 1%, which lines up with the calculated IFRs of similar early-breakout locations when treatments were still in their infancy.
That doesn't suggest to me that something like that could happen in the US now, by and large their outbreak happened before people took the virus seriously and they were extremely late to react. They also had the issue of multi generational housing and an older population. They were probably undergoing something close to the true R0 of 2.5 during their outbreak, whereas in the US the places that are "outbreaking" are peaking at R_t of 1.1-1.3.
But, to me it is reasonable evidence that there is not some magical barrier at 20% infection where the virus dies out regardless of what behaviors we pursue. I think we are just seeing that 20% infection of the population, in combination with other behavior changes, testing, tracing, etc. is probably enough to have sustained R_t <1.
I don't want to agree, I've hoped there was something to this 20% infection thing. And I still do hope, but I have questions. When rate of new cases rises quickly is when societies tend to enact measures to slow the spread, it's not an unmodified petri dish were only one variable - the virus - is introduced.
I've been watching Brazil and wondering when they might hit the downside of new cases and deaths. What is always unknowable is how many people REALLY had the virus, we only know how many have a confirmed case (and I guess you could even question that) and have to estimate how many we think have contacted it. Because NYC antibody testing seemed to indicate 10x those who had tested positive actually had antibodies (2% vs 20%), I started using the 10x number - but it's going to vary based on degree of testing in a country or region.
In the US, 51.2 million tests have uncovered 4.1 million cases. In Brazil, only 4.9 million tests have been run yet 2.2 million cases - they've been running at a nearly 50% test positive rate for most of this time. That makes me thing they have maybe 20x the actual cases. if looking at their death - 83,000, and assuming an IFR of 0.5, That would mean 16.6 million have contracted the virus - less than 8x actual confirmed. I guess they are targeting their tests well or have run way more tests then they have revealed. 16.6 million is not yet even 10% of their population, so they have a long way to go.
Using US deaths of 146,700 and assuming an IFR of 0.3% (better health care), that would mean maybe 49 million americans have had the virus, roughly 15% of population.
Of course IFR matters hugely, I've seen recent estimates of 0.1 to 1.2% and that would drastically change any attempts to calculate a true infected count from the # of deaths.