Thursday, January 27, 2022

Numbers and Covid-19


There are two numbers that matter in an epidemic. The R(0) which is the infectivity estimate, and lethality, F.

The R(0) number is the expected number of new people who will be infected by each currently infected person. Oddly these are not totally independent. For example, imagine a virus that is so lethal that a human cannot transmit because they die too fast. So, a new virus like SARS-COV-12 started from an external host (still unknown), and spreads to humans from humans because it is not instantly lethal.

The March 17th 2020 R(0) US National rate for the coronavirus was 1.2, and F= ~3.5%.
The R(0) had stabilized at 1.17 in the summer of 2020.

Of course people decided to party again.
So cases spiked back with the 2020 Winter Holidays to R(0) of 3.8, and the F= 1.89%.

Vaccinations start in earnest January 2021. There were 184,179,469 US residents vaccinated by July 1, 2021. Infectivity, and fatality rates were all falling.  

Then Delta happened.
The July 1, 2021 R(0) was 1.18. It peaked at 7 day R(0)= 1.22  F=1.7%. By Sept. 30, 2021 it had even dropped to R(0) 0.7, F=1.3%

By December the Omicron variant in the US spiked to 3x the maximum number of Delta cases.

It has been since early Dec. 2021 that the Omicron variant has been the predominant SARS-COV-2 virus in the US. It also seems to have peaked. If things continue as current trends suggest, the Omicron death rate will be an amazing low of the Delta LOW. That is an F= 0.33% of confirmed cases.

Some folks will think, "Well - that is trivial. What is the big worry?"

The worry is that the R(0) is 2.98. The net deaths have not changed, while hospitals are filled to the roof tops.