You can find a study that says pretty much anything, but what you should be looking for is scientific consensus. Most studies have herd immunity at 60% or greater.
https://www.sciencemediacentre.org/e...herd-immunity/
Herd immunity can be estimated from the R0 value with this formula: 1 - (1 / R0). For example, for herd immunity to be reached at 20%, this is the equation: 1 - (1/1.25) = 0.2. The R0 of the virus would have to be 1.25, which is lower than the flu. The R0 of the flu is ~1.6 (which means ~40% herd immunity).
And I think we all know that this virus is more contagious than the flu.