Unfortunately, we can't rely on flattening or plummeting curves to predict herd immunity: we had both in the summer, remember. Assuming that immunity lasts at least a few months once you've had the virus (unsafe, but hey), and that the vaccine stalls transmission as well as preventing illness (unsafe, but hey), and that restrictions help to keep the reinfection rate low (more likely than not but not settled science), we could see a sharp tailing-off of cases in the next few months. I'm up for hanging on to that one...