[timr]

R0 is not a constant inherent to a virus strain. It's a contextual number, determined by population and behavior, population immunity and other factors.

Rt is simply notation of an estimate of R0 at a particular time.

Either way, you're correct that "herd immunity", as used here, means the point at which time the infection rate begins to decline, and this is conditional on population behaviors. If people mix more freely, the estimate changes.

However, the observation that people don't mix uniformly still applies, even if they mix a bit more than they do now. To put it in a CS context, it's like debating the magnitude of the constant, when the algorithm has a fundamentally different asymptotic behavior.

[jupp0r]

> R0 is not a constant inherent to a virus strain. It's a contextual number, determined by population and behavior, population immunity and other factors.

From Wikipedia: In epidemiology, the basic reproduction number, or basic reproductive number (sometimes called basic reproduction ratio or basic reproductive rate), denoted {\displaystyle R_{0}}R_{0} (pronounced R nought or R zero),[20] of an infection can be thought of as the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection.

https://en.wikipedia.org/wiki/Basic_reproduction_number

[whoisburbansky]

The next paragraph calls out that R0 is not a biological constant specific to a pathogen as it is affected by environment and behavior.

[watwut]

> can be thought of as the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection

Yeah, and that is contextual number, determined by population behavior and other factors.

Yes, population immunity should not be on that list, but the population behavior, weatcher and what not are still influencing it a lot.

[timr]

Population immunity has to be on the list: if the population has some level of immunity, it affects the observed R0. And we can't really measure immunity, other than in very crude ways (i.e. antibody tests for specific epitopes), so we can't control for it.

This isn't a political statement of any sort.

[timr]

You can think of it that way, but we never know, in practice, what level of actual immunity exists in a population.

In any case, it's not relevant to my point: R0 is a contextual number, always defined by empirical data. It's not a fixed feature of the virus.

[jacquesm]

Exactly. OP is simply wrong about this.