"As soon as you get the influenza vaccine your body starts to build an immunity to it. So, although it takes two weeks to build up your full immunity to the influenza virus, you are immediately receiving the benefits," says McCasland.
McCasland says 37 people with the flu are hospitalized in intensive care units in Sacramento County.
She says even more people may have died from the flu, but state and local health departments don't keep track of flu deaths in the 65-and-over population.
Povery-striken, densely packed neighborhoods in the Sacramento region were hit hardest by this year's flu, according to a newspaper analysis.
The number of flu-related deaths has increased again in California -- by 35 in the past week -- bringing the total number of deaths to 278 this season.
California is reporting almost twice the number of flu-related deaths as last year.
California health officials are reporting the rate of illness from influenza is higher than normal for this time of year, with a more dangerous form of the virus leading the way.