A-L-E-X wrote:Source of the post I wonder if there is a quantitative comparison about how much more contagious it is vs the original.

What I have read is that Delta is about 50% more transmissible than Alpha (the UK variant), which was about 50-70% more transmissible than the original. So if R

_{0} for the original virus was between 2 and 3, then for Delta it is between 5 and 8, with a most probable value of about 6.

I also checked with a simple model what value of R

_{0} gives a best fit for recent outbreaks such as in the UK, the Netherlands, and in parts of the US with certain vaccination rates, while also accounting for some immunity by recovery from prior infection. Basically, the data tell me the same thing: Delta's R

_{0} cannot be less than 4, and most likely it's around 6.

It is kind of bothering me that media continues to cite the "70% threshold to reach herd immunity". That's simply not true anymore with how transmissible Delta is. We see Delta spreading in places with more than 70% vaccination + recovery. This could also be an effect of how unvaccinated people are more likely to socialize with other unvaccinated people. Despite being a very good toy model, the spread of a virus through a population is more complicated than a bunch of dots randomly moving around and bumping into each other, and in this case that complexity matters.