https://arxiv.org/abs/2005.03085 - The disease-induced herd immunity level for Covid-19 is substantially lower than the classical herd immunity level

https://www.medrxiv.org/content/10.1101/2020.04.27.20081893v... - Individual variation in susceptibility or exposure to SARS-CoV-2 lowers the herd immunity threshold

This effect will be amplified if the initial vaccinations are given (as they should be) to the potential superspreaders, like healthcare workers and essential manual laborers.