Measles cases have been reported in 21 U.S. states, including California. The majority of people affected by the disease were unvaccinated and the untreated infection can result in encephalitis, swelling of the brain, and even death. In addition, this year’s outbreak has surpassed 2017’s record of 118 cases.

From Jan. 1 to July 14, measles cases have been reported primarily in the East Coast, West Coast, and the midwestern United States. In the most recent case, a 16-year-old-girl visiting Alaska on a cruise was contagious and actively spreading the disease. She had contracted measles from a previous trip to Thailand, and Alaska state health officials are concerned about the number of people she came in contact with on the cruise ship.

The majority of people infected in the 21 U.S. states were unvaccinated. 97% of the time, measles can be prevented with two simple MMR vaccines (measles, mumps, and rubella). However, with the new circulating idea that vaccines can cause disorders like autism and ADHD, fewer children are getting the needed medical protection. Measles can spread easily when an infected person coughs or sneezes, and the disease is even more dangerous when it comes upon an unvaccinated community. If one person has it, nine out of the ten people around him or her will become infected if they are not protected.

At its current pace, the current measles outbreak could be the worst since 2014, when a staggering number of 667 people were infected. Because the measles virus was eradicated completely in the U.S. in 2000, all new cases came from travelers. Measles is still common in many parts of the world including countries in Asia, Europe, the Pacific, and Africa.

Symptoms of the measles virus occur seven to fourteen days after infection. They include watery eyes, runny nose, and a high fever. As the disease progresses, white dots called Koplik spots begin appearing on the inside of the person’s mouth. The most well-known symbol of measles, the red rash, will be accompanied with an extremely high fever. Untreated, measles can eventually cause death.

The Centers for Disease Control and Prevention (CDC) are urging hesitant parents to give their children the necessary vaccinations. “Widespread use of the measles vaccine has led to a greater than 99% reduction in measles cases compared with the pre-vaccine era,” the CDC said. Federal health officials are still investigating and trying to prevent another catastrophic outbreak.