[Petrochemicals (OP)]

I cannot find reliable numbers for transmission rate under normal conditions.

[set fair]

Best I could find is

What is the R0 for Covid-19?

The World Health Organization (WHO) estimated at the start of March the R number was between 2 and 2.5, but estimates from different studies vary widely.

According to nine studies in China and South Korea between December and March, the mean estimated R number is 2.63, the CEBM said.

https://www.itv.com/news/2020-04-28/coronavirus-q-a-what-is-the-r-value

[evan_au]

You can compare it with established R₀ values for various diseases at the following web page.
- They mention a rather wide range for COVID-19, but the figure from alancalverd agrees with figures I have seen.
https://en.wikipedia.org/wiki/Basic_reproduction_number

Of course, the goal is to get R₀ down below 1 by measures like wearing face masks, social distancing, minimizing the size of gatherings, working from home wherever possible and restricting long-distance travel. 

...and (eventually), by vaccination.

[alancalverd]

There are no "normal conditions".

We have seen effective R values around 10 where a sneezing carrier works closely with several people, and zero where a potential spreader isolates himself until he is virus-free. Even the 10 value is based on symptomatic victims, which is why entire schools, colleges and factories have been closed when a single source is identified, lest everyone else become an asymptomatic carrier.

The published value is a national average derived from the historic ratio of diagnosed cases from one day to another.   

[Bored chemist]

I cannot find reliable numbers for transmission rate under normal conditions.

If anyone tried to measure it, the ethics committee would (rightly) put a stop to it.

So the best you will get is an estimate- of "about 2 or 3".

Imagine that I somehow was able to tell you that the answer is actually 2.56 +/- 0.03
What would you do with that data?

[alancalverd]

A very good reason for not having an effective testing regime is that tests only increase the reported value of R. This obvious fact was broadcast by the scum in front of the White House several months ago.

Incidentally we do have sound, ethical and scientifically useful values of R for sexually transmitted diseases, because most people can remember who they had sex with. But not many COVID-infectious Members of Parliament can remember who else was on the train to Edinburgh. 

[Bored chemist]

Incidentally we do have sound, ethical and scientifically useful values of R for sexually transmitted diseases

True (well- as good as self reported data ever gets).
But it's not because those people "tried to measure it".

[alancalverd]

Not the spreaders, nor the victims, but some really expert NHS testers and tracers, who have been comprehensively sidelined so that Cummings' friends and donors can get big contracts for failing to even measure COVID.