COVID-19 again on the rise in Sonoma County

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COVID-19 transmission in Sonoma County is once again on the rise, largely driven by an increase in new cases among unvaccinated residents, local health officials said Friday.

While so-called “breakthrough“ infections continue to occur among those who have been fully vaccinated, these rates have been stable for more than a month, hovering at between five and seven new daily cases per 100,000 residents, according to county data.

By comparison, the same rate among the unvaccinated increased steadily through the month of October, from about 18 to 28 new daily cases per 100,000 people.

“It’s the unvaccinated who are driving the pandemic,” said Dr. John Swartzberg, a UC Berkeley infectious disease expert. “They’re the ones who are getting infected and spreading the virus to the rest of the community.”

Swartzberg pointed out that Sonoma County has the largest transmission rate increase in the Bay Area, according to The New York Times’ COVID-19 case counts. Sonoma County’s daily infection rate per 100,000 residents increased by 75% in the past 14 days.

All nine Bay Area counties reported transmission rate increases over the past two weeks, though nothing as large as Sonoma County. San Mateo and Alameda counties reported the next largest increases, 36% and 23%, respectively.

“Something is going on in Sonoma County,” said Swartzberg. “It looks like Sonoma is going in the wrong direction.”

Napa County has among the smallest case rate increases in the past two weeks, at 4%. Though Contra Costa County has seen only a 2% increase in COVID-19 transmission during this period, that county has among the second highest rates in the Bay Area, with a 7-day average of 114 new cases per 100,000 residents.

Kathryn Pack, health program manager for Sonoma County's epidemiology team, said the recent uptick in cases mirrors the rise in cases seen at this time last year. She said contributing factors include increases in school cases and gatherings, particularly in entertainment venues and among friends and family, as well as Halloween festivals.

Pack said there is growing concern about the possibility of even more virus spread during the winter months, as more people gather and travel for the holidays and spend more time indoors. Pack said the recent increase in cases comes after a period of decline and brief stabilization that followed the summer surge.

Dr. Sundari Mase, Sonoma County’s health officer, agreed that unvaccinated people are the principal driver of rising cases. She said that although vaccinated residents do become infected, virus spread is more aggressive among the unvaccinated who contract the virus.

“The reason we say this is a pandemic of the unvaccinated is simply because you’re much more likely to get COVID if you're unvaccinated,” Mase said. “If you're unvaccinated, you're probably five times more likely to get COVID ... than the vaccinated person.”

Mase said that when vaccinated individuals contract the virus, they’re far less likely to become severely ill. That means “they're less likely to transmit the virus, so it breaks that chain of transmission,” she said.

This week, health officials reported another two deaths linked to COVID-19. For the past four weeks, county public health staff have reported two COVID-19 deaths each week. During the summer, officials were reporting virus-related deaths every few days.

The decrease in pandemic deaths tracks with the decline in new COVID-19 cases and hospitalizations since the summer wave of infections and deaths. Swartzberg, the UC Berkeley infectious disease expert, said he fears another winter surge of infections, though not as severe or deadly as last year’s, is possible.

The latest two fatalities, which bring the total local pandemic death toll to 408, include a vaccinated woman between 80 and 90 who died Oct. 26 and an unvaccinated woman 60 to 70 who died Sept. 16. Both had underlying health conditions.

You can reach Staff Writer Martin Espinoza at 707-521-5213 or On Twitter @pressreno.

For information about how to schedule a vaccine in Sonoma County, go here.

To track coronavirus cases in Sonoma County, across California, the United States and around the world, go here.

For more stories about the coronavirus, go here.

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