Herd immunity in the U.S.? San Francisco offers reasons for optimism


Adam Bergeron is looking forward to reopening the Balboa Theater, the independent movie theater in San Francisco he owns and operates.

He’s watched as other movie theaters around the U.S. welcomed audiences back ahead of his. But San Francisco has been slower to reopen than other cities. Now, the time feels right.

“San Francisco’s been a model for doing Covid the right way, if there is such a thing,” Bergeron said.

“At this point, everyone I know is completely vaccinated. The cases are going down. And we just chose a time that seemed like it was going to be the right time,” he added. He’s planning to reopen May 14 with a “Godzilla” marathon.

San Francisco and its suburbs have been cautious, maintaining various restrictions while other parts of the country reopened businesses and eased mask mandates. Meanwhile, its vaccination rate is among the highest of any major U.S. city, with two-thirds of all adults having received at least one dose.

And as parts of the city open up — some San Francisco bars have waitlists to get a table again — experts are offering a cautious optimism. The city may be seeing signs of herd immunity.

“This is our moment to put the pandemic behind us,” said Dr. Grant Colfax, San Francisco’s health director. “It’s clear that the vaccines are our way out of this.”

Herd immunity is about transmission. If enough people can’t catch and spread a virus, particularly in a community that already has few cases, the virus struggles to find new hosts. Eventually, infections would naturally taper off. It’s a simple concept, yet it can be elusive and difficult to define — particularly at the national level.

Locally, though, it can be clearer. Over the past seven days, San Francisco, home to more than 870,000 people, recorded an average of only 26 new Covid-19 cases per day. Two-thirds of all adults in San Francisco and almost 60 percent of the greater metro area of 4.7 million have been vaccinated with at least one dose — one of the highest rates in the U.S. Its positive test rate sits at 1.2 percent.