More than 80% of people who are vaccinated got their vaccination more than six months ago, which means protection is waning for millions of people as we head into the holiday season.
The CDC last month recommended anyone 65 years or older, as well as adults with underlying medical conditions or who work in high-risk jobs, get a COVID-19 booster shot.
In San Francisco, at this point, only around 1 in 3 eligible seniors have heeded that call.
"We're starting to see hospitalizations in that group — even though they have been vaccinated — and some deaths," infectious diseases specialist Dr. Peter Chin-Hong said.
Across California, fewer people have been getting boosters than anticipated.
State officials are now trying to give boosters a boost, asking health providers to get proactive in their outreach and ordering that for anyone 18 or older, they "not turn a patient away who is requesting a booster."
That exceeds federal guidelines, as the FDA is still considering Pfizer's request for emergency authorization of its booster for all adults.
California's move to open booster shot eligibility to millions comes amid, once again, a rising number of infections and, from the governor, a rising level of concern.
"We enjoyed the summer where we had the lowest case rates in the summer for a large portion of the summer. Just yesterday we went up to about 16th lowest," Gov. Gavin Newsom said. "That moved rather quickly. I say that not to alarm people, but to caution folks."
The governor's push to vaccinate is meeting pushback. Protesters gathered on the San Francisco side of the Golden Gate Bridge to protest against vaccine mandates.
In California, and nationwide, doctors are becoming less hopeful that enough people will get vaccinated to end winter waves of the virus.
"We're going to navigate this new world where infections are going to happen," Chin-Hong said. "We're moving from an epidemic or pandemic situation to endemic, where it's probably going to surge every winter as a new normal.
Because, it appears, COVID isn't going away anytime soon, and boosting the immune systems of the already-vaccinated up to snuff is rising as a public health priority.
"If you got your vaccine more than six months ago and you got breakthrough infection, you might be protected if you're otherwise healthy and younger," Chin-Hong said. "But it doesn't mean that you won't carry infection that may then spread to someone else."