What is Measles?

Measles is a vaccine-preventable, highly communicable (easy to spread) disease caused by the measles virus. The reason why measles is so contagious is because the virus is easily spread through the air, by coughing and sneezing, as well as direct contact with an infected person [1]. The incubation period (time from exposure to first symptom) for measles is about 10 days. The characteristic measles rash appears within about 14 days following exposure. Individuals with measles are infectious from approximately 4 days before rash onset until 4 days after the rash appears. According to the CDC “Measles is so contagious that if one person has it, 90% of the people close to that person who are not immune will also become infectious” [3]. Consequently, anyone who has not had measles or been successfully immunized is susceptible to the disease. About 30% of measles cases result in complications, such as pneumonia, diarrhea, and ear infections [1,2].


Re-Emergence of Measles in the United States

An ongoing measles outbreak in California has drawn lots of media attention, but isn’t the only measles outbreak the United States has seen in recent years. Data from the last few years show a drastic increase in measles cases. In 2014 alone, the CDC’s National Center for Immunization and Respiratory Diseases reported 644 cases across 27 states* [4].

Prior to the “Disneyland Outbreak”, California saw an increase in measles cases and between January and October 6, 2014 there were 61 measles cases in California [8]. The majority of the primary cases were linked to unvaccinated individuals returning from travel to the Philippines, where there had been a reported outbreak [12, 13]. These individuals then infected others.


Disneyland Outbreak

Although measles was eliminated in the United States in 2000, it is still a common disease, with occasional outbreaks in other parts of the world [13, 14]. Not only can Americans traveling to measles-endemic countries bring it back to the United States, but tourists traveling with a measles infection can import and spread the disease within the United States as well [13]. California houses many sights and attractions, therefore it is a popular tourist destination, and a measles vaccination is not required for travel to the United States. When measles reaches a population where even a small proportion of individuals are unvaccinated, an outbreak can occur. This appears to be the cause of the ongoing measles outbreak in California, which has been linked to the Disneyland theme parks located in Anaheim, California [5,9].

The current outbreak is believed to have begun when an individual infected with measles visited Disneyland and/or Disney California Adventure exposing susceptible theme park attendees and employees to the virus between December 15 and December 20, 2014 [8]. Of the original six cases that became infected at Disneyland, three were children and three were adults. All of the children and one of the adult cases were unvaccinated, one of the adults was partially vaccinated, and one was fully vaccinated [7]. Health authorities recommend that children be vaccinated between 12 and 15 months. The live attenuated measles vaccine results in active immunity in 94% to 98% of susceptible individuals. A second dose can increase immunity to 99% and is therefore recommended for children prior to starting school, i.e. approximately 4 to 6 years old [1]. The measles vaccine was licensed in 1963, but the recommendation for a second dose to boost immunity did not become protocol until 1998, following a resurgence of measles that occurred in the United States between 1989 and 1991. These cases were occurring among school-aged children who had received one dose of the measles vaccine [14].

The Disneyland outbreak has since grown as infected individuals come into contact with and expose susceptible people to the virus. It is also believed that additional infectious individuals visited the theme park again in January 2015, resulting in more infections [6].

As of January 21st, 2015, the California Department of Public Health states that there have been 59 confirmed cases among California residents in 2015 [6, 10]. Forty-two of these cases have been linked to the initial measles exposure in December at Disneyland [6, 10]. Furthermore, five of the confirmed cases are Disney employees. The measles cases have expanded past Anaheim and are currently scattered throughout the state. Information on vaccination status is known for 34 of the 59 cases, with 82% of those 34 cases being unvaccinated. (To see more: http://www.cdph.ca.gov/HealthInfo/discond/Pages/Measles.aspx)

Measles cases outside of California have been linked to the Disneyland outbreak [10]. Utah has had 3 cases (2 primary, 1 secondary); Washington has had 2 cases (1 primary, 1 secondary); Colorado has had 1 case, Oregon has had 1 case; and Mexico has 1 case [10].  On January 24 CBS released an article stating that the number of measles cases has increased to 85 and now covers a total of 7 states, including Arizona and Nebraska [11].

Additional suspected cases are under investigation by the California Department of Public Health. It is important to note that California state epidemiologist, Dr. Gilberto Chavez, has recommended that unvaccinated individuals and parents with infants too young to receive the vaccination stay away from Disneyland [11]. It is also recommended that unvaccinated individuals, or individuals who are uncertain about their vaccination status, contact their provider to receive the vaccination as soon as possible. The California Department of Public Health has declared that they expect to see more measles cases over the new few weeks [5].



  1. David L. Heymann. 2008. Control of Communicable Diseases Manual. 19th Edition. American Public Health Association.
  2. http://www.cdc.gov/measles/
  3. http://www.cdc.gov/measles/about/transmission.html
  4. http://www.cdc.gov/measles/cases-outbreaks.html
  5. http://www.nbcnews.com/health/health-news/disney-measles-outbreak-could-get-worse-experts-warn-n291426
  6. http://www.cdph.ca.gov/Pages/NR15-008.aspx
  7. http://www.latimes.com/local/lanow/la-me-ln-disneyland-measles-outbreak-grows-sparks-concern-20150110-story.html
  8. http://www.latimes.com/local/california/la-me-aa2-snapshot-measles-whooping-cough-20150108-story.html#page=2
  9. http://www.sfgate.com/health/article/Disneyland-measles-outbreak-spreads-to-Bay-Area-6031212.php
  10. http://www.cdph.ca.gov/HealthInfo/discond/Pages/Measles.aspx
  11. http://www.cbsnews.com/news/measles-outbreak-traced-to-disneyland-continues-to-grow/
  12. http://wwwnc.cdc.gov/travel/notices/watch/measles-philippines
  13. http://www.cdc.gov/measles/about/faqs.html
  14. http://www.cdc.gov/vaccines/pubs/surv-manual/chpt07-measles.html

*Alabama, California, Colorado, Connecticut, Hawaii, Illinois, Indiana, Kansas, Massachusetts, Michigan, Minnesota, Missouri, Nebraska, New Jersey, New Mexico, New York, North Carolina, Ohio, Oregon, Pennsylvania, South Dakota, Tennessee, Texas, Utah, Virginia, Washington, and Wisconsin.



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