S.F. virus cases rival state rate
Power of delta variant seen, even in city with high vaccination levels
Coronavirus cases rose faster in San Francisco in the past week than in the Bay Area and California as a whole, and the city’s case rate on several days exceeded both the region’s and state’s.
It was a rare occurrence for the city, which has had among the lowest virus rates among major U.S. metropolitan areas throughout the pandemic.
Experts say that more than a month after the state — and the city — reopened, the super contagious delta variant is spreading rapidly among the unvaccinated.
Dr. Jahan Fahimi, an emergency room doctor at UCSF, said cases have been climbing there among those who are unvaccinated, as well as patients who were fully vaccinated but are immunocompromised.
“Even in a place like San Francisco with really high vaccination rates, we’re seeing a surge because this virus is basically going out there and finding every unvaccinated person,” he said.
The number of new cases
recorded over the past seven days in San Francisco was up 81.6% from the previous sevenday period, according to the California Data Coalition, whose case counts power the Chronicle Coronavirus Map. New cases in California over the past seven days were up 71% from the previous period, and across the Bay Area that number was 61%.
San Francisco’s case rate also slightly exceeded the Bay Area’s and California’s on several days over the past week — most recently on Tuesday, when the city’s rate was 11.7 per 100,000, the Bay Area’s was 10.6 and California’s was 11.5.
As of Thursday, San Francisco’s sevenday average of new cases was 13 per 100,000 people, while the California sevenday average case rate was 13.7 and the Bay Area’s was 12.5.
In San Francisco, 69% of residents are fully vaccinated, according to the county’s dashboard. In California, 52.4% are fully vaccinated, according to Centers for Disease Control and Prevention data on The Chronicle’s COVID19 vaccine tracker.
The San Francisco Public Health Department said in a statement that the city tends to test more people than many other places around California, which could be one factor in its higher case rate right now. The statement continued, “As a city, we are prioritizing testing in our hardesthit areas to detect disease. As the second-densest city in the country, we know viruses that are highly transmissible will spread quicker within the community.”
Dr. Robert Wachter, chair of the UCSF Department of Medicine, said that the numbers — while worse than he thought they would be a month ago — are “not a disaster,” but indicate that even in areas with high levels of vaccination, the unvaccinated are still at significant risk.
“What the last month has demonstrated is that even threequarters of a population vaccinated in the face of a virus that’s twice as infectious is not enough to prevent significant amounts of spread,” he said.
Dr. Julie Parsonnet, an epidemiologist at Stanford, said that while vaccinated people shouldn’t be worried by these numbers, they do indicate that herd immunity — the idea that enough people would be vaccinated to stop the spread of the virus — is out of reach.
“It seems likely to me given these patterns that people who are vaccinated are capable of transmitting” even if they don’t get sick, she said. “So if you’re not vaccinated, you’re going to get the virus.”
“We need to vaccinate everyone to protect the people who are at the highest risk,” she added.
San Francisco is also seeing higher “breakthrough” case rates among vaccinated people than California as a whole. In San Francisco, there are 5.8 cases per 100,000 vaccinated residents and 15 cases per 100,000 unvaccinated, according to county officials. These rates are both higher than the state, which reported 2 cases per 100,000 vaccinated residents and 13 for unvaccinated.
On Jan. 13, during the worst of the winter surge before vaccinations became widespread, San Francisco’s case rate peaked at 40.7 per 100,000 residents. The statewide rate peaked a day later at 110.2 cases per 100,000.
Parsonnet said that while it’s still unclear why San Francisco’s rate would be higher than the state as a whole, some reasons might include that San Francisco is more crowded than other areas and that the city was spared early on, so fewer people have natural immunity. Still, she said, the differences between the case rates are relatively small.
Case rates have been going up since California’s reopening on June 15. But experts stress that even with these rising case rates — and breakthrough infections — the vaccines are working as intended. Unvaccinated people make up over 99% of deaths and hospitalizations, according to state officials.
San Francisco has not reported any deaths among vaccinated residents, and death rates in the city and the Bay Area remain low.
“The vaccines are meant to prevent the severest consequences of COVID and they’re doing a great job with that,” said Dr. Naveena Bobba, San Francisco’s deputy director of health. “Given the unvaccinated rate in San Francisco, even if it is small, we have 300 deaths that could happen if it remains at the current rate.”
“The power of the vaccine isn’t necessarily in preventing infection,” Dr. Peter ChinHong, an infectious disease expert at UCSF, said. “It’s in preventing people from getting really sick.”
Fahimi’s hospital staff has seen a few breakthrough cases. He said doctors and nurses are bracing for an increase in patients if this wave follows the trajectory of previous surges.
“Fortunately, delta hit at a time when the majority of individuals are vaccinated. We did dodge a bullet in that sense,” Fahimi said. “But now what we’re seeing is this rapid spread, and when this many people get infected we’re going to see surges in all of the other negative outcomes we were hoping to avoid.”
“It hasn’t happened yet, but our numbers are slowly creeping up as the cases rise,” he added. “We’re curious where this will go.”
Parsonnet said that while case rates will likely continue to go up, this surge will likely not reach the levels seen in the winter. She does not think the state or the Bay Area should go back into lockdown, but said that increased masking will likely help.
Vaccinations are still the only way out, she said.
“There’s no excuse for not getting vaccinated” if you can, she said. “That there are deaths from this disease now is really inexcusable.”