There's good news and bad news about Covid-19.
By simple division, using reported cases and deaths, the CFR in New York City is 10.8%. But both cases and deaths are under-reported. Probably, cases should be higher by a factor of 10 and deaths by a factor of 2. That would make the CFR about 2%.
There is some hope that the CFR in the US as a whole will be somewhat less. It's hard to say, lack of rural hospital capacity is a huge issue. Let's call it 1%.
That's still bad news, it's about 10x the big flu epidemics in 1956-57 and 1967-68.
Covid is reasonably hard to catch. Epidemiology studies suggest that most transmissions occur in the home, to family members or others who have extended close contact with the infected person. Even then, with an infected person in the home, the probability of transmission is less than 20%.
However, mass transit and restaurants are places where some transmissions do occur.
The possibility of aerosol (rather than just droplet) transmission has been suggested, but this seems quite a low hazard based on estimates for the transmission ratio R of 2.5-3. It would be a lot higher with transmission via aerosols.
I think wearing a mask indoors in public is a good idea (to prevent transmission from you to others), but a mask while walking on the beach or riding your bike it just silly.
More good news is that there is very little asymptomatic transmission, although there is significant pre-symptomatic transmission. 40-50% of transmission happen before symptoms occur. With the mean time to onset of symptoms at 5 days, people are infectious from 1-2 days before to 5 days after. PCR+ results from after that are not actually viable virus.
And, with aggressive lockdowns, testing and tracing, it is possible to eliminate the virus. (New Zealand, Hong Kong, South Korea, Iceland, etc.) Whether that's permanent or not we'll see.
However, in the US we have chosen a different path. Both the President and conservative media have propagated the (false) idea that this is just the flu and the lockdown is unnecessary. Add to that our natural rebelliousness. The lockdown has only slowed but not stopped transmission.
The federal government has deliberately chosen not to develop increased testing capacity (so as to keep the apparent number of cases low), nor to develop tracing capability. This could still help, even with if the epidemic continues.
Cases are level in the US as a whole, and some counties in the Midwest are increasing cases really rapidly.
Now we're "opening up".
I think what that means is that we really will go on to infect 50-75% or more of the country. Estimates on the time for that range from 6 months to 2 years.
During that time I think we can expect 0.01 x 0.50 x 330M = 1.65M deaths. That's about half the loss experienced in the 1918-20 pandemic. I would not be surprised to be off by a factor of 2 either way.
Caveats:
- Covid may slow down in the summer, but it doesn't seem likely.
- We may develop more effective treatments. Remdesivir early could be a great thing, but it's hard to make.
- The vaccine candidates that are least likely to be highly efficacious are the ones that will come first, perhaps in 6-8 months (nucleic acid vaccines). But even a not-so-great vaccine could help with the CFR.
