California Gov. Jerry Brown issued an emergency proclamation Friday that will allow the state to increase its supply of vaccines amid a hepatitis A outbreak that has killed more than a dozen people.

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Two cases of Hepatitis A linked to Santa Clara County jails The outbreak involves more than 570 of cases in San Diego, Santa Cruz and Los Angeles counties. In San Diego County, 490 people have fallen ill and 18 people have died from the liver disease since March of this year, according to the California Department of Public Health.

In Los Angeles County, 13 people have fallen ill, according to county health officials.

It’s the worst hepatitis A outbreak in the United States transmitted from person to person — instead of by contaminated food — since the vaccine became available in 1996. California health officials say the majority affected are homeless, using drugs or both.

“We cannot wait until more communities are infected and impacted before taking action.” — U.S. Rep. Darrell Issa, the San Diego-area Republican writing to the U.S. Health and Human Services Department and the Centers for Disease Control and Prevention

Brown’s proclamation gives state health officials the authority to immediately purchase vaccines directly from manufacturers and distribute them to impacted communities.

“Vaccination is the best way to prevent infection from the hepatitis A virus,” Gil Chavez, deputy director of the state department’s Center for Infectious Diseases, told reporters during a conference call Friday.

Hepatitis A is a liver disease with symptoms that include fever, fatigue, loss of appetite, nausea, vomiting, abdominal pain, dark urine, clay-colored bowel movements, joint pain, and a yellowing of the skin or eyes or jaundice. In extreme cases, the virus can cause liver failure and even death.

The virus is spread from person-to-person through close contact or through contact with environments contaminated with feces. Hepatitis A is not airborne, meaning it cannot be acquired by breathing the same air as an infected person.

“You have to touch a surface that is contaminated,” to contract the virus, Chavez said. “We always advise people that they should always practice good hand hygiene.”

Chavez said the state has been able to provide about 80,000 doses of the hepatitis A vaccine to at-risk communities through a federal program run by the Centers for Disease Control and Prevention.

“That is a big chunk of their total supply for the entire country for the year,” Chavez said. “It’s been very clear that our continued requests for additional vaccines is running into their limit with what they can share with California.”

What are the symptoms of Hepatitis A? pic.twitter.com/cBSOK3Kcfh — Los Angeles County (@CountyofLA) September 19, 2017

He added that state health officials don’t yet know how many more vaccines they will need to end the outbreak or how much money the state has to spend on vaccines. The tens of thousands of doses already administered were provided by the CDC for free.

The Associated Press reported that U.S. Rep. Darrell Issa on Friday called on the federal government to provide emergency funding to halt the spread of hepatitis A. He said the outbreak has brought statewide totals to three times the number of reported cases in 2015.

“We cannot wait until more communities are infected and impacted before taking action,” the San Diego-area Republican wrote to the U.S. Health and Human Services Department and the CDC.

A message left by the Associated Press seeking comment from the CDC wasn’t immediately returned.

Chavez expected to be able to order additional vaccines as early as Monday or Tuesday.

Vaccination against hepatitis A has been recommended for all children in California since 1999. The vaccine is highly effective and can last as long as 20 years, Chavez said.

“One dose provides a high level of immunity,” he said.

The Associated Press contributed to this report.