Contra Costa County health officials confirm a 48-year-old woman died of the H-1, N-1 strain.
This comes after the flu killed a 41-year-old woman in Santa Clara County last week. Three people have also died in Sacramento County.
Few details are being released about the victims but we do know the woman who died in Contra Costa County had other, underlying health problems.
Officials say they've seen 17 severe cases of the flu in Contra Costa County so far.