All Bay Area Counties Are Back In CDC’s Top Two Tiers For Covid Transmission

Jamie Ferrell Jamie Ferrell

All Bay Area Counties Are Back In CDC’s Top Two Tiers For Covid Transmission

The Bay Area leads the state in terms of high vaccination turnout and low hospitalization rates, but all counties have now returned to the CDC’s top two tiers for COVID transmission. Last week, October 26 transmission rates showed many counties in the yellow “moderate” tier, including San Francisco. But as of yesterday, November 2, all have experienced a spike in transmission rates.

Bay Area Covid transmission, last week on October 26, 2021. Via CDC Covid Data Tracker.
Bay Area Covid transmission, yesterday on November 2, 2021. Via CDC Covid Data Tracker.

At the moment, orange “substantial” transmission counties include San Francisco, San Mateo, Marin, Napa, Contra Costa, Alameda, Santa Clara, and Santa Cruz. Sonoma and Solano Counties are now in the red “high” transmission tier.

The CDC measures Covid transmission based on two metrics: the number of new cases per 100,000 people in the previous 7 days, and the percentage of positive NAAT tests in the previous 7 days.

  • Red “high” transmission means ≥100 cases, or ≥10% positive tests
  • Orange “substantial” transmission means 50-99.99 cases or 8-9.99% positive tests
  • Yellow “moderate” transmission means 10-49.99 cases or 5-7.99% positive tests
  • Blue “low” transmission means ≤10 cases or ≤5% positive tests.

San Francisco County is currently in the moderate orange category, having recorded a 65.91% case rate during the last 7 days. At last count, 89% of SF residents 12 and older have received at least 1 vaccine dose and 84% have completed the series.


The vaccines prove highly effective against severe illness, hospitalization, and death from Covid-19. Check out these CDC resources to learn more.


Featured image: CDC Covid Data Tracker

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