California now has 59 confirmed cases of measles, 42 of which are linked to visits to Disneyland theme parks in Southern California in December, according to the California Department of Public Health (CDPH).

“We are off to a bad start in 2015,” Dr. Gil Chavez, deputy director of the Center for Infectious Diseases with the CDPH, told reporters Wednesday. “Measles is not a trivial illness.”

The most recent case related to the Disney outbreak was diagnosed on Jan. 18. The infected patients range in age from 7 months to 70 years, and include five Disney employees. A quarter of the patients have been hospitalized, Chavez said.

Symptoms of measles include fever, cough, runny nose, and red eyes before progressing into a telltale red rash. In some cases, the illness can be fatal.

“If you have symptoms, and believe you may have been exposed, please contact your health care provider. Unless you have an emergency, it is best to contact your health care provider by phone to prevent spread in doctor’s offices,” Dr. Ron Chapman, director of the CDPH, said in a statement.

He added, “The best way to prevent measles and its spread is to get vaccinated.”

Read More About the Disneyland Outbreak »

Measles: A Preventable Infection

Measles is a highly infectious, airborne disease that’s most easily prevented with two doses of the measles, mumps, and rubella (MMR) vaccine. More than 80 percent of those infected, whose vaccination status could be documented, were not immunized. Six of those infected were too young to get the vaccine.

“We have a particular responsibility to protect our infants who are too young to be immunized,” Chavez said. “Vaccines are proven to be safe and effective.”

Vaccination against measles has been recommended since 1989. Because of widespread vaccination, measles was eliminated from the United States in 2000. Cases that occur now are usually brought in from other countries.

Those who are fully vaccinated with two doses of the MMR vaccine shouldn’t have any concerns about being in densely populated areas that attract international visitors, such as Disneyland. Those who aren’t vaccinated, however, are susceptible for as long as two hours after an infected person has come and gone from the area.

“If you’re not vaccinated, places where a lot of people congregate may not be safe,” Chavez said. “Get immunized and you won’t have to worry about it.”

Still, the MMR vaccine is only 99 percent effective, which is why five patients infected in California were either partially or fully vaccinated.

Learn More About the Vaccines Children Need »

Clusters of Unvaccinated Kids Raise Outbreak Risk

According to a recent study published in the journal Pediatrics, about 3 percent of California’s population opts out of the recommended vaccination schedules. But they are not spread evenly across the state.

In certain areas of California, unvaccinated children make up more than 20 percent of the child population.

Researchers found that the pockets are often geographically small, such as a 1.8-mile area in Vallejo where 22.7 percent of children were unvaccinated. Other areas at risk include places in or around El Cerrito, San Francisco, and Sacramento.

“That becomes a huge problem in the state,” Chavez said of the low vaccination rate.

Many parents do not vaccinate their children for fear that it may be harmful. They often cite a well-known 1998 study that suggested vaccines cause autism, which has since been retracted and thoroughly debunked.

California has a new law on the books that requires parents who wish to opt out of school vaccination requirements to see a qualified medical professional who will present factual, evidence-based information about the safety and efficacy of vaccines.

In the year since the law took effect, Chavez said progress has been made “little by little” in reversing the tide of vaccine denial.

“There is absolutely no evidence that vaccines are in any way dangerous to children or adults,” Chavez said.

Learn More About the Paranoia Surrounding Vaccines »