Confused about a COVID reporting stat

Not a Disney question, but you guys seem to know a lot about this stuff.

What does Rt value mean? And what is R0?

Both mean Reproduction Rate. I believe they are used interchangeably.

It represents the number of new infections estimated to stem from a single case.

In other words, if R0 is 2.5, then one person with the disease is expected to infect, on average, 2.5 others.

An R0 below 1 suggests that the number of cases is shrinking, possibly allowing societies to open back up. An R0 above 1 indicates that the number of cases is growing, perhaps necessitating renewed lockdowns or other measures.


This is a really interesting question so I looked it up.
I think @darkmite2 is right about R0, as far as I could tell the only difference between it and Rt is that Rt is more geographically and temporally narrow. I guess you could say Rt is a very specific R0.

Here’s a neat real-time chart that shows the Rt in any given state in the US.


So, yesterday, my area had an Rt of .86. Today, it’s 1. That’s bad for us, right?

But right next door to us and even closer to the mega-city than we are, where we shop and interact, their Rt is .73, down from yesterday.

I guess the numbers are based on the counts of the day and maybe fluctuate easily, but it’s discouraging.

Going up from 0.86 to 1 is bad, but I’d guess the daily numbers, particularly for a small population, are incredibly noisy. I’d look more at a 7 day rolling average, if available, to see if things are getting better or worse as the numbers should be a lot less noisy. 'Course you need to wait awhile for the updated numbers…

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This is us for the last week:

One distinction I’ve read is the R0 is the reproduction rate absent any interventions or mitigating factors. R0 for a given virus strain does not change (absent mutation). R (without the naught) is the reproduction rate including the impact of any interventions. R can vary by location and time due to implementation and removal of measures.

Rt I assume is R at a given place and time?


Oh dear, here in Mexico we barely gave number of deceased… and we can’t even get that right! I’d panic with these metrics!

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