SAN FRANCISCO (KGO) -- California issued updated masking guidance Wednesday, recommending everyone remain masked indoors, regardless of vaccination status. But, there are a few counties that may be first in line.
The announcement follows guidance first modified by the Centers for Disease Control and Prevention (CDC) this week as coronavirus cases and hospitalizations continue to surge across the country and in the Bay Area.
"Mandating masks is the next step," said UCSF epidemiologist Dr. George Rutherford. "Transmission will likely be driving that decision."
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ABC7's data team is tracking the level of community transmission across every county in California. In the Bay Area, there are four counties colored in red, indicating transmission is considered "high." The list includes: San Francisco, Contra Costa, Alameda and Solano counties. All four counties reported between a 30 to 70 percent increase in COVID cases over the past seven days. To put it in perspective, collectively the four counties reported 5,531 cases and 367 hospitalizations in one week.
CDC COVID-19 Transmission Categories by California County
Map not displaying correctly? Click here to open in a new window.
Stephanie Sierra: "Do you think these counties could be first?"
Dr. Rutherford: "It would make sense, the people with the worst problems would do it first."
The remaining five Bay Area counties are colored in orange, indicating community transmission is "substantial."
Stephanie Sierra: "How would you rank the top three factors driving most of this transmission?"
Dr. Rutherford: "First and foremost, lack of vaccinations, the second is the Delta variant, and then we get down to the third thing --- indoor transmission. Most of the transmission occurring is indoors... going on in households. But if we're going to go outside of households, I think bars and clubs are next on the list."
Stanford Infectious Disease Dr. Jorge Salinas expects a decision on a mask mandate may not happen immediately as health officials may need more time to assess the data.
VIDEO: Bay Area doctor lists 4 main reasons why he believes everyone should mask indoors again
"We need to recognize that there are delays in between the moment people get infected, develop symptoms, and then severe symptoms that require hospitalizations," Salinas said,
But, Salinas added the need for a mandate is more crucial now as CDC data shows vaccinated people who are re-infected with the virus are just as transmissible as those unvaccinated.
"If you're vaccinated, you'll be in better shape, but you can still get infected and spread the same amount of virus as those who aren't," he said. "This is why masks are so important for everyone right now."
Most Bay Area counties are currently recommending masking indoors regardless if you're vaccinated, but an announcement involving a potential mandate could be coming soon.
"I think it could happen within a week," said Rutherford. "I would imagine they may decide to do it collectively or they may decide to do it individually. So, we'll see."
ABC7 reached out to every Bay Area county for further comment but we are awaiting specific details on an announcement.
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