This is a daily updated tracker website providing time-varying estimated reproduction numbers for COVID-19 in California, based on both daily case counts and wastewater readings.

We estimate transmission rates of COVID–19 using reproduction numbers. A time-varying reproduction number, commonly written R, is the average number of cases infected by a given case over the course of that individual’s disease progression. Of particular interest is the question of whether transmission is supercritical, meaning that R > 1, in which case the epidemic can increase in size, or is subcritical, meaning that R < 1, in which case it will fade out. To eliminate a disease locally, it is not necessary to reduce R to zero, only to reduce it below one for a sustained period.

We use raw data from three sources: new cases by county from California Health and Human Services, (“Cases”, below); wastewater readings from the Cal-SuWers network (“Wastewater (C)”), WastewaterScan (“Wastewater (W)”), and BioBot Analytics (“Wastewater (B)”).

For more details see the Methods section below.

Recent

R estimates

This is a plot of estimated reproduction numbers in the Bay Area. For the complete timeseries, see the csv data linked below. The latest estimates are as follows: in Alameda County, from NA, 1.02 on June 13, 2024; in Contra Costa County, from NA, 1.02 on June 17, 2024; in Marin County, from NA, 1.02 on June 17, 2024; in Napa County, from NA, 1.02 on June 17, 2024; in San Francisco County, from NA, 1.02 on June 18, 2024; in San Mateo County, from NA, 1.02 on June 18, 2024; in Santa Clara County, from NA, 1.00 on June 18, 2024; in Solano County, from NA, 1.01 on June 17, 2024; in Sonoma County, from NA, 1.01 on June 17, 2024.

This is a plot of estimated reproduction numbers in the Bay Area. For the complete timeseries, see the csv data linked below. The latest estimates are as follows: in Alameda County, from NA, 1.02 on June 13, 2024; in Contra Costa County, from NA, 1.02 on June 17, 2024; in Marin County, from NA, 1.02 on June 17, 2024; in Napa County, from NA, 1.02 on June 17, 2024; in San Francisco County, from NA, 1.02 on June 18, 2024; in San Mateo County, from NA, 1.02 on June 18, 2024; in Santa Clara County, from NA, 1.00 on June 18, 2024; in Solano County, from NA, 1.01 on June 17, 2024; in Sonoma County, from NA, 1.01 on June 17, 2024.