The most accurate statement about herd immunity among the provided options is: Herd immunity is the turning point of an epidemic.
Herd immunity refers to a situation where a sufficient percentage of the population is immune to an infectious disease, either through vaccination or previous infections, which reduces the overall amount of the disease in the population and provides indirect protection to individuals who are not immune. This can help control and eventually turn the tide of an epidemic, but it does not necessarily mean the end of a pandemic or that the population can go back to normal immediately.