Measles was declared eliminated as a circulating disease in the United States in the year 2000.1 However, importation of measles into the U.S. from other countries where the virus remains endemic continues to be a threat. The U.S. Centers for Disease Control and Prevention (CDC) recently reported that there have been 288 confirmed cases of measles so far this year (January 1 – May 23, 2014).2 This total breaks the previous YEARLY record of cases since measles was declared eliminated (the prior record was 220 cases in 2011). This number also includes the largest outbreak in the U.S. since elimination (138 cases and counting in Ohio).3 Congratulations U.S.A., you have broken a yearly record, and it’s only June! Way to go!
Why are we seeing so many cases of measles this year?
Measles was eliminated in the U.S. through vaccination.4 The current measles vaccine is part of the measles-mumps-rubella (MMR) triple-vaccine given to children at the age of 1, with a second (booster) shot given just before they enter elementary school (between the ages of 4-6).5 Although uptake for the MMR vaccine is fairly high overall across the U.S. (>90% of adolescents have been vaccinated), there remain pockets of unvaccinated individuals through which measles can spread.2,6 The current outbreak in Ohio started among a large pocket of unvaccinated Amish – several individuals visited the Philippines for humanitarian reasons, but unknowingly contracted the virus and brought it back to the U.S. where it quickly circulated.7
And it’s not just certain religious groups that are not vaccinating. Although vaccination is required for enrollment in public schools, 48 states allow parents to opt out of vaccinations for religious or philosophical reasons via personal belief exemptions (PBEs). Like-minded parents tend to live in the same neighborhoods and send their children to the same schools, creating pockets of intentionally unvaccinated kids. A 2010 study found that in five California counties (Sutter, Mendocino, Nevada, Humboldt, and Santa Cruz), more than half of vaccine-exempted kindergartners were enrolled in schools with an opt-out rate of more than 20%.8 Sixty of the measles cases confirmed this year have been in California.2
Why you should care about measles
Before the vaccine, “an estimated 3–4 million persons in the United States were infected each year, of whom 400–500 died, 48,000 were hospitalized, and another 1,000 developed chronic disability from measles encephalitis.”9 Measels is an infection caused by a paramyxovirus (genus Morbillivirus). Humans are the only host. The primary site of infection is the respiratory tract, from which the virus spreads to the lymph nodes and other organs. 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. It is highly communicable: 90% of unvaccinated people exposed to measles will catch it. To put it in perspective, my sister came down with measles in 1990 when she was 14 years old (she was partially vaccinated, having never received a booster), and how she contracted it remains a mystery. At the time, Philadelphia was experiencing a measles epidemic, so the most likely explanation is that she caught measles while at the mall or grocery store (although getting it at the R.E.M. concert at the Spectrum would have made for a better story10). None of our family or friends, and none of her classmates, had measles.
Measles symptoms4 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 out of 1000 cases) and death (1-2 out of 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. Measles is not a benign disease.
Vaccination remains our best defense against measles
There is no benefit in delaying childhood immunizations and, for the MMR vaccine, delaying the shot has actually been found to increase the risk of febrile seizures.11,12 The CDC also recommends that unless there is evidence of immunity, adults, especially those that are planning to travel internationally, should receive at least one dose of the MMR vaccine.13Adults who are unsure of their measles immunization status can get a titer test (which consists of a blood draw) from their primary care physician. A second (booster) shot for measles was not recommended until 1989, so if you are an adult over the age of 35, chances are you have received only a single dose of measles vaccine. The MMR vaccine has 95% efficacy after the first shot, and 99% efficacy following the booster. Still, this means that for every 100 people vaccinated, a few will not mount an immune response and will remain unprotected. These unprotected people (and those that cannot be vaccinated due to medical conditions) rely on the rest of us to get vaccinated and break the cycle of person-to-person transmission (a concept called herd immunity).
For the record, I practice what I preach. I received an MMR booster in 1990 when my sister was diagnosed with measles. My husband was titer tested for measles before a trip to Poland. Most importantly (to me), my daughter was vaccinated on-time according to the CDC schedule. The World Health Organization (WHO) has a goal of measles elimination in 5 of the 6 global regions by 2020.14 The WHO Region of the Americas (which contains the U.S.), is already there and has sustained measles elimination since 2002. Let’s not go backwards. Get vaccinated, and we may never have to talk about measles again.15
References/ Further Reading
1. Katz SL, AR Hinman. 2004. Summary and conclusions: Measles elimination meeting, 16–17 March 2000. J Infect Dis. 189:S43–47.
6. Fiebelkorn AP, SB Redd, K Gallagher, et al. 2010. Measles in the United States during the postelimination era. J. Infect. Dis. 202:1520-1528.
11. Smith MJ, CR Woods. 2010. On-time vaccine receipt in the first year does not adversely affect neuropsychological outcomes. Pediatrics. 125: 1134-1141.
12. Hambidge SJ, SR Newcomer, KJ Narwaney, et al. 2014. Timely versus delayed early childhood vaccination and seizures. Pediatrics. pii: peds.2013-3429. [epub ahead of print]