It is fun to imagine the negative herd immunity threshold implied by the erroneous form of the equation though :P
Say R0 is 2, 1/(1 - R0) means that we already hit herd immunity before SARS-CoV-2 even existed!
The frightening one for me was R0 == 1: Basically, we'd need a positive or negative infinite percentage of people to be infected depending on which direction you approach it from.