How can you tell if you're protected against the measles?

The measles outbreak in Southern California has raised a lot of questions about what it means to be protected. The criteria is different for children versus adults.

For adults: The Centers for Disease Control and Prevention considers you protected if you received one dose of the measles vaccine and you're not in a high-risk setting for measles transmission.

A high-risk setting includes: students at post-high school educational institutions, people who work in healthcare and people travelling internationally, for example.

MORE: Many of those susceptible to infection are college age

If you're an adult in a high-risk setting, you need to have received two doses of the measles vaccine.

You're also protected if a lab test confirms you had measles at some point in your life.

And, if you were born before 1957, you're considered protected.

MORE: Measles outbreak in Southern California: Everything you need to know

Do adults need a booster shot? The CDC says no. Their experts say people who received two doses of measles vaccine as children, according to the U.S. vaccination schedule, are protected for life and they do not ever need a booster shot.

If you think you were exposed to measles, call your doctor immediately.

They can determine your immunity based on your vaccine history, or through a lab test.

The measles is so contagious, the virus can live for up to two hours in an airspace where an infected person has coughed or sneezed.

According to the CDC, if one person has the measles virus, up to 90 percent of people close to that person, who are not immune, will also become infected.