The Minnesota Department of Health has confirmed a ninth case of measles in the state.

While they're all located in Hennepin County, health officials say the vaccination is critical to stopping the spread.

This year has seen the most cases of measles in Minnesota since 2011 and the second most in the last 20 years according to the Minnesota Department of Health.

Minnesota Department of Health Director of Infectious Disease Division Kris Ehresmann said, "We typically have one to two cases a year, but to have nine cases in unvaccinated kids is really concerning and really serious."

The cases are in unvaccinated children ages one through four years old, and since they are younger, these cases can be more severe.

Symptoms of measles include a high fever, cough, runny nose and watery eyes followed by a rash.

It's highly contagious and spreads easily, even by being in the same room with someone who has measles.

Mayo Clinic Health System Mankato Infectious Disease Physician Assistant Jessica Sheehy said, "They found that it's just a highly virulent organism that can be transmitted very easily unlike other organisms that can take several hours of close contact to be transmitted."

The Department of Health says all but one case was in the Somali population, which has a lower vaccination rate.

Health officials add this outbreak was preventable with the two doses of the Measles, Mumps and Rubella or MMR vaccine which can be as effective as 97 percent.

But one concern is more people have opted to go without the shot, increasing the spread.

Sheehy said, "There are larger pockets of people who have not been vaccinated; this decreased the herd immunity, so chances are these types of illnesses can spread much more easily."

Department of Health is expecting to find more cases in the coming weeks because it can take up to two weeks for symptoms to appear.

Ehresmann said, "We know that there have been multiple other exposure settings that they were at that they could have transmitted to other people."

According to state records, Minnesota's MMR vaccination rate is about 90 percent.

While the virus is no longer common in the United States, there are still many cases across the world.

Anyone who has not been vaccinated, the vaccine is recommended before traveling outside of the country.

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--KEYC News 12