“Hepatitis A is a vaccine-preventable illness,” said the Kentucky Department of Public Health (DPH) acting commissioner Dr. Jeffrey Howard in a statement. “DPH recommends all children, ages 1 year through 18, receive the Hepatitis A vaccine, as well as adults who want to prevent themselves from an acute Hepatitis A infection. In these counties with local transmission of the Hepatitis A virus, we recommend everyone be vaccinated per guidelines to help stop this outbreak.”

Subscribe to Brainstorm Health Daily, our newsletter about the most exciting health innovations.

Hepatitis A has been spreading at an alarming rate through Kentucky’s Jefferson, Bullitt, Hardin, Greenup, Carter, and Boyd counties, infecting more than 300 people and killing at least one. The Hepatitis A virus attacks the liver, causes flu-like symptoms, and is highly contagious. It can be transmitted through contact with an infected person or from tainted water and food.

Some medical experts stressed that now may be as good a time as any to get vaccinated given that tens of thousands of people from around the world will soon be flocking to the state for the Kentucky Derby in early May. Although the full recommended vaccination schedule involves two doses six months apart, an initial dose given now would significantly boost Hepatitis A immunity before the Derby, which draws crowds in excess of 150,000.

Last fall, San Diego faced its own deadly Hepatitis A outbreak, which killed more than a dozen people and hit its homeless community particularly hard. Many adults may not have received their Hepatitis A vaccines because it wasn’t always a public school requirement in all states.