18 cases of the highly transmissible delta COVID-19 variant detected in Sonoma County

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Sonoma County public health officials on Monday said they have detected 18 cases of the delta strain, a more contagious mutation of the coronavirus that is spreading rapidly across the United States and has already led to some European officials reinstating or extending pandemic restrictions.

The delta variant, first identified in India in December, is believed to be 50% more transmissible than the UK variant, which itself was 50% more transmissible than the early strain of coronavirus, said Dr. John Swartzberg, a UC Berkeley infectious disease expert.

“This particular virus, the delta variant, is more transmissible than anything we have faced so far,” Swartzberg said. “In the United Kingdom it’s causing a surge of cases, and it’s occurring in people who are not vaccinated primarily or undervaccinated.”

According to the latest local tally of COVID-19 mutations, the delta strain now accounts for 6.8% of the 265 coronavirus variant infections detected in Sonoma County as of June 21. The previous count on June 15 had the number of delta cases at 3 of 223 total cases, or only 1.3%.

Local public health officials say they are keeping a close eye on the rise of the delta strain, a trend that is being seen across the state and country.

Dr. Kismet Baldwin, the county’s deputy health officer, said the rise of the delta strain, technically known as B.1.617.2, is a reminder that the coronavirus pandemic is not over yet, especially for those who have not yet been vaccinated.

Local residents should continue to follow pandemic-related precautions where they still exist, including public transportation centers, mega events, correctional facilities, and shelters. Baldwin emphasized the importance of getting vaccinated, as current coronavirus vaccines offer significant protection against the delta mutation.

“Getting vaccinated is still a great idea,” she said. “There’s been some preliminary data from the UK that’s showing that the Pfizer and AstraZeneca vaccines do provide efficacy against the delta variant after you’ve been fully vaccinated.”

Swartzberg said one shot of the Pfizer or Moderna vaccines is likely to only give about 30% protection against the delta variant. In contrast, he said studies have shown that a fully vacccinated will receive a range of protection between 70% and 88%.

As June 20, 65% of Sonoma County residents 12 and older have been fully vaccinated.

The largest share of local variants are the so-called West Coast strains, B.1.427 and B.1.429, now called epsilon variants. These account for 130 of the 265 detected variant cases.

There are 29 cases of the U.K. variant, B.1.1.7. and 4 cases of P.1, also known as the Brazilian variant.

Swartzberg said Sonoma County, the Bay Area and much of California are not likely to be as affected by the rise in delta variant cases as are other parts of the United States that have much lower vaccination rates. Southern states are going to “see a real problem,” he said.

“I don’t think we’re going to see a marked surge like we saw last summer, at the end of July, certainly not here,” he said.

Baldwin, who is in charge of tracking coronavirus variants in the county public health division, said it’s too early to tell what impact the growing number of delta variant cases will have on the current move to reopen the state and local economies.

“It’s too early to comment or speculate on what effect it’s going to have,“ she said. ”I think the more people who get vaccinated the better, the less likelihood of us having any kind of surge in the future.“

Swartzberg agrees. The way to prevent coronavirus variants from becoming a problem is to get vaccinated, he said. Every time the virus is passed from one person to another, there’s a chance it will mutate.

“If you’re vaccinated, you’re not going to be a variant factory,” he said.

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

EDITOR’S NOTE: This story has been revised to clarify a quotation from Dr. John Swartzberg.

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

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

For more stories about the coronavirus, go here.

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