Over the past year, San Francisco and its suburbs have maintained various pandemic restrictions while other parts of the country reopened businesses and eased mask mandates. Now, with a relatively low new Covid-19 case count and its vaccination rate among the highest of any major U.S. city, San Francisco may be seeing signs of herd immunity, experts say. Other cities are likely not far behind. But achieving herd immunity doesn’t automatically guarantee the coronavirus will simply fade away, and one expert says herd immunity should not be thought of as the end goal. | 