Last year was a banner year for measles in the United States. The CDC’s provisional number of measles cases for 2014 stands at 644, the most since measles was declared eliminated from the USA 14 years earlier.1 Over half the states in the union experienced measles. It appears that 2015 is picking up right where 2014 left off. During the 2014 winter holiday season, an unknown person infected with measles vacationed at the Disneyland/ California Adventure theme parks in California, and while there, infected several people.2 Among those infected was an unvaccinated California woman who then traveled by air from Orange County, CA to Washington State in late December 2014, and then flew back to Orange County on January 3, 2015.3 Measles, a highly infectious, airborne disease, had now been in two airports across two states. It’s also suspected that another individual contracted measles at Disney and then attended the Rose Bowl, putting hundreds more people at risk.4

As of Wednesday, January 21, 2015, there are 54 cases and counting associated with the Disneyland outbreak, including 5 Disney employees.5,6 Over 40 of the cases are in California, with additional cases in Colorado, Utah, Washington, Oregon, and Mexico.7,8 California is one of the WORST places for a measles outbreak, as unvaccinated individuals tend to cluster among neighborhoods.9 A recent scientific paper, “Geographic Clusters in Underimmunization and Vaccine Refusal,” examined over 150,000 children born in Northern California between the years 2000-2011 and found 5 clusters of significant under-immunization (defined as missing one or more of the CDC-recommended vaccines by age 3).10 Within these clusters, the under-immunization rate was 18-23%, compared to 11% outside them. Likewise, vaccine refusal rates ranged 5-13% within clusters and 3% outside. How do these clusters occur? A record number of California parents opted out of vaccinating their kids in 2014.11 Although vaccination is technically required for enrollment in public schools, 48 states (including California) allow parents to opt out of vaccinations for religious or philosophical reasons via personal belief exemptions. Oregon, also affected with a case of measles stemming from this outbreak, has the highest rate of vaccine exemptions for children.12

What the sign outside Disneyland SHOULD say
What the sign outside Disneyland SHOULD say

With the Disneyland measles outbreak, we have a highly contagious disease that’s been brought into a region where there are pockets of highly unvaccinated, and therefore disease-susceptible, individuals. Measles is spread person-to-person through sneezing and coughing, and the virus can survive in the air or on surfaces for about 2 hours.13 Ninety percent of unvaccinated people exposed to measles will catch it. One study estimates that an unvaccinated person is 35x more likely to catch measles than a vaccinated person.14 Indeed, of the first 7 reported cases of measles in this outbreak, 6 were completely unvaccinated (including two infants too young to receive the vaccine) and only one had the recommended 2 doses of MMR vaccine.2 So here we have a case where the majority of people at Disneyland were vaccinated (about 90% of the general population is vaccinated against measles), yet the majority of people who caught the virus were unvaccinated. This outbreak is yet another example of how the unimmunized fuel disease spread and erode herd immunity.15,16

California is also home to two pediatricians well-known for pandering to the anti-vaccine movement. Dr. Jay Gordon, famous for being the pediatrician of actress and anti-vaccine activist Jenny McCarthy’s son, has stated on his Twitter feed that in light of the recent outbreak, he will give MMR (reluctantly) to those over the age of 3 if the parents ask.17 Why age three? Because he believes it to be safer, with absolutely no evidence to support this view. Scientific evidence actually suggests the opposite: delaying the shot has actually been found to increase the risk of febrile seizures.18,19  Dr. Bob Sears takes this a step further. As author of the best-selling “The Vaccine Book,” he touts a different schedule for vaccinations than that recommended by the CDC. “The Vaccine Book” is the thorn in the side of many pediatricians, as the Sears schedule leaves children either unimmunized or partially-immunized for longer periods of time, thus making them more susceptible to disease. In fact, Sears stated in a news interview that half of his clients were unvaccinated.20 On his Facebook page this week, Sears downplays the measles as not serious and nothing to be worried about.21 This rhetoric by Sears parrots a common anti-vaccine trope best laid out in the children’s book, “Melanie’s Marvelous Measles.” This book, written by staunch vaccine opponent Stephanie Messenger, portrays measles as not bad at all, unless you eat junk food and (ironically) get vaccinated.22

In my previous post on measles,23 I outline the symptoms and complications: “Measles symptoms13 include high fever, cough, runny nose, sore throat, and conjunctivitis. A small cluster of white lesions inside the mouth (called Koplik’s spots) precedes the rash on the outer skin by 1-2 days. The tell-tale red measles skin rash does not appear until around 2 weeks after exposure and lasts about a week. Diarrhea, ear infections, and pneumonia are common complications of measles. More severe complications include encephalitis (1 in 1000 cases) and death (1-2 in 1000 cases). A quarter of those who suffer from measles encephalitis will also experience neurological damage. Measles infection during pregnancy results in a higher risk of premature labor, spontaneous abortion, and low-birthweight infants.” Before the measles vaccine, 3–4 million individuals were infected each year in the US, of whom 400–500 died, 48,000 were hospitalized, and 1,000 developed chronic disability.24 Measles as marvelous? I think not. On the other hand, complications resulting from MMR immunization vaccine13 include fever (1 in 10 doses) and rash (1 in 20 doses). Twenty five percent of adult women administered the vaccine may experience joint pain. Encephalitis and severe allergic reactions to the MMR are rare (less than 1 in 1,000,000 doses). The MMR vaccine has 95% efficacy after the first shot, and 99% efficacy following a second, “booster,” shot. Still, this means that for every 100 people vaccinated, a few will not mount an immune response and will remain unprotected against the disease. These unprotected people (and those that cannot be vaccinated due to medical conditions) rely on high rates of vaccination within the general population so that the disease cannot spread. When too many people opt out of getting immunized, diseases such as measles which were once gone now reemerge.15,16 The Disneyland outbreak is poised to teach us once again that we cannot let our guard down against disease.

References/ Further Reading
10. Lieu TA, et al. 2015. Geographic Clusters in Underimmunization and Vaccine Refusal. Pediatrics. doi: 10.1542/peds.2014-2715. [epub ahead of print] 11.
14. Salmon DA, et al. 1999. Health consequences of religious and philosophical exemptions from immunization laws: individual and societal risk of measles. JAMA. 282:47-53.
18. Smith MJ, CR Woods. 2010. On-time vaccine receipt in the first year does not adversely affect neuropsychological outcomes. Pediatrics. 125: 1134-1141.
19. Hambidge SJ, et al. 2014. Timely versus delayed early childhood vaccination and seizures. Pediatrics. 133:1492-1499.