> What is the mortality rate of one of the more severe stains of the common cold or the flu?
One of the more severe strains of the flu? 10% globally (1918 H1N1 pandemic flu, estimated 500 million infected, 50 million killed), about 2% in the US.
> I'm sure we've had one of those that got to 0.5% or more in recent history?
No, and certainly not one that also was a global pandemic. I mean, the 2009 H1N1 pandemic swine flu had, in the US, about 0.02% mortality. Typical seasonal flu has a 0.1% mortality rate. The common cold is a syndrome caused by a variety of viruses (mostly rhinoviruses, but I think the next most common are coronaviruses.) If we had a relative of one of those that produced serious health impacts with any frequency, we wouldn't call it the common cold, but, e.g., COVID-19.
> Does that mean 0.5% is too low to shut everything down?
The mortality rate alone is not the measure. You need to consider the health system burden per infection (because if you saturate that system, mortality goes up, and not just for the infection causing the above-normal saturation.) And you need to consider how infectious the disease is, and what the transmission vectors are. And you need to consider the incidence of severe-but-nonfatal effects.
One of the more severe strains of the flu? 10% globally (1918 H1N1 pandemic flu, estimated 500 million infected, 50 million killed), about 2% in the US.
> I'm sure we've had one of those that got to 0.5% or more in recent history?
No, and certainly not one that also was a global pandemic. I mean, the 2009 H1N1 pandemic swine flu had, in the US, about 0.02% mortality. Typical seasonal flu has a 0.1% mortality rate. The common cold is a syndrome caused by a variety of viruses (mostly rhinoviruses, but I think the next most common are coronaviruses.) If we had a relative of one of those that produced serious health impacts with any frequency, we wouldn't call it the common cold, but, e.g., COVID-19.
> Does that mean 0.5% is too low to shut everything down?
The mortality rate alone is not the measure. You need to consider the health system burden per infection (because if you saturate that system, mortality goes up, and not just for the infection causing the above-normal saturation.) And you need to consider how infectious the disease is, and what the transmission vectors are. And you need to consider the incidence of severe-but-nonfatal effects.