Sonoma County Public Health officials said this week that hospital and nursing facility workers who work in a "high-risk settings" must now get a flu shot every fall.

Those who decline the vaccine will be required to wear a surgical mask throughout the five-month flu season, which runs from Nov. 1 to March 31. This year, the rule takes effect Dec. 15.

The new public health order, announced this week by Lynn Silver-Chalfin, the county's public health officer, is similar to measures taken by officials in San Francisco, Sacramento, Santa Clara and Alameda counties.

The order applies to acute-care hospitals, skilled nursing homes, residential care for the elderly, residential developmental centers and dialysis centers. The order strongly recommends vaccination for other types of health care workers, but it does not require workers in clinics or outpatient facilities to wear masks.

The measure is aimed at preventing the transmission of the flu virus to elderly or sick patients being cared for in the hospital or a nursing facility.