Dr David Fisman, an epidemiologist at the Dalla Lana School of Public Health and a friend of mine, recently made these graphs on herd immunity.

The vaccine uptake we need to see to achieve herd immunity is based on vaccine efficacy & reproduction number of the dominant variant in circulation. With Delta, numbers needed to vaccinate are very high and almost unattainable, therefore it is so critically important to vaccinate as much as we can & continue certain (but likely not all) public health measures.