In general, herd immunity is the number of people who need to have immunity to protect people who are within the herd who do not have immunity. Whether you get it through having had the disease or being vaccinated, it's that protective sort of effect.
Herd immunity for a virus can be anywhere from 50% to 90% of people who need to be vaccinated. Certainly with respect to COVID-19 and the SARS-CoV-2 virus, when we were first looking at it, I think we were looking at estimates of around 60% to 70% that we would require being vaccinated. Now with the emergence of variants and because they are more transmissible, I think a lot of people are adjusting those numbers up towards more like 85%, or even potentially 90%, coverage to achieve herd immunity. Certainly it's a moving target, because as we know, the virus and its transmissibility, and how contagious it is, is changing.