In California, the Department of Public Health reports 61 confirmed cases of measles so far this year - that's more than three times the amount reported the same time last year, and the second highest in the country.The U.S. is seeing a rise of measles cases and experts say it could be due to the fact that parents aren't vaccinating their children as much.This year the CDC reports as of August 25, there have been 592 confirmed cases in 21 states. As you can see by this chart, that's a big difference from previous years.In fact, the Los Angeles Times reports parents in the state are deciding against vaccinating their kindergarten-age children at twice the rate they did seven years ago, despite it being a state law.And in other states like Idaho, Illinois, Michigan and Vermont more than 4.5% of kindergartners last year were unvaccinated for non-medical reasons.Measles is a highly contagious viral disease. It begins with a fever and is followed by an itchy rash along with several other uncomfortable symptoms. Most children get vaccinated around the time they turn 1, then again before they begin kindergarten.From 2 to 5 percent of people don't respond to their first dose of the vaccine... But more than 99 percent of people develop immunity to measles after two doses, which is why it can be very helpful. So why the push back?There are a couple of reasons. Some believe the vaccinations can cause autism in their children, a theory scientists have not supported. Other parents believe there are more benefits to feeding their children a healthy diet, rather than treating them with medicine. Even celebrities like Jenny McCarthy and Aidan Quinn have voiced support for the anti-vaccination movement.Currently Ohio has the largest number of confirmed measles cases with at least 138 reported.Also on AOL: