There was one death reported in Solano County today after a Vallejo man in his 40s was infected with the H1N1 strain, or "swine flu."
His was the first flu death of the season in that county.
The man had chronic medical conditions before he fell ill, county health officials said.
There have been also been 10 people hospitalized in the county with swine flu and other strains of influenza, according to health officials.
A third flu-related death was reported today in San Mateo County. The second was reported Monday, county health system spokeswoman Robyn Thaw said.
Two of the three patients that died had underlying medical conditions and at least two of the cases were H1N1, according to health officials.
In Sonoma County, a 54-year-old died in the county's second flu-related death. A 23-year-old had died from the flu earlier this season.
In additional to those fatalities, there have been four deaths in Santa Clara County, three in Alameda County and two in Marin County. There has been one death each in Contra Costa, Santa Cruz and San Francisco counties.
Swine flu, which first emerged in 2009, is known to be more dangerous to young and middle-age adults than other strains of the flu.
Health officials are urging everyone ages 6 months and older to get vaccinated.
The peak of flu season is between January and March, and the vaccine takes about two weeks after inoculation to be fully effective, according to health officials.