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California Gov. Brown declared a state of emergency Friday because of the state��s hepatitis A outbreak that has killed at least 18 people.

“Vaccinating people at risk of exposure is the most effective tool we have to prevent the spread of hepatitis A infection during an outbreak,” said California Department of Public Health Director Dr. Karen Smith.

The department has already distributed about 80,000 doses of the vaccine, but officials said they need more to address the outbreak. The emergency declaration will allow the health department to purchase more vaccine doses and distribute them to more people who are at risk, officials said.

Hepatitis A is commonly transmitted through contaminated food. The only U.S. outbreak in the last 20 years bigger than California’s occurred in Pennsylvania in 2003, when more than 900 people were infected after eating contaminated green onions at a restaurant.

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