It would be difficult not to notice the many reports of measles occurring in the United States this year. Between January 1 and May 20, 2011, the Centers for Disease Control and Prevention received reports of 118 cases of measles. Most of the cases (89%) were associated with importation of the infection from outside the United States.
We have to look back to 1996, before the elimination of measles in the United States, to find more measles cases in the same number of weeks. That year, the CDC recorded a total of 508 cases. The median number of U.S. measles cases in each of the past 10 years has been 56, so this year’s figures are already markedly higher.
The measles virus is extremely contagious: on average, 90% of those exposed to someone with the measles will get the disease themselves unless they’ve been vaccinated, or have had measles before. Combine that with international travel at unprecedented levels, measles outbreaks occurring all over the world, and pockets of unvaccinated individuals in the United States, and it’s not surprising that we’ve seen so many U.S. cases this year. The map below from the CDC shows the clusters of measles cases since January 1.
The largest measles cluster occurred in Minnesota, and was centered in a Somali community. This group has received nationwide attention because of its apparently high autism rate and its connection to Andrew Wakefield, MD, who made a discredited connection between measles vaccination and autism. Many members of the Somali community in Minneapolis, fearful of autism, have refused measles vaccination for their children. Wakefield has met with the Somali community in Minneapolis several times in the past year, beginning in December 2010.
In February, an unvaccinated Somali infant became infected with measles on a trip to Kenya, and this led to 20 more cases in the Minneapolis area. (Two other cases occurred through separate importations.) Of the 23 total cases, seven were infants too young to be vaccinated, nine people were of age to be vaccinated but were not, one was vaccinated, one was vaccinated but earlier than the recommended age, and five had an unknown vaccination status. The outbreak resulted in 14 hospitalizations.
Outbreaks in France
France, meanwhile, is experiencing its own measles resurgence (though the disease had never been eliminated there). From January through April of this year, about 10,000 cases were reported in France, with complications from measles including 6 deaths, 12 cases of encephalitis, and 360 cases of severe measles pneumonia. A World Health Organization official, quoted in an Associated Press report, said, “There’s been a buildup of children who have not been immunized over the years. It’s almost like a threshold. When you have enough people who have not been immunized, then outbreaks can occur.” Indeed, a BBC report states that only 85% of France’s preschool-aged children have been vaccinated against measles, far lower than the approximately 95% coverage needed to protect a community against this highly contagious virus.
The scope of measles in the United States before the vaccine is astounding. According to the CDC, “In the decade before the measles vaccination program began, an estimated 3–4 million persons in the United States were infected each year. Of these, 400–500 died, 48,000 were hospitalized, and another 1,000 developed chronic disability from measles encephalitis.” (Press Releases, August 21, 2008). Measles was so widespread, and such a common childhood illness, that anyone born before 1957 is assumed to be immune to the disease because of prior exposure.
Globally, the burden of measles remains high. In 2008, 164,000 people, mostly children under age 5, died of the disease. Global reported cases in 2009 were 222,408, though the number of suspected cases is much higher. To address the problem, WHO, the United Nations Foundation, the CDC, the American Red Cross, and UNICEF launched the Measles Initiative. The group’s efforts have ensured that more than 700 million children have been vaccinated for measles. Global routine measles vaccination coverage is now around 83%, though India, Nigeria, Ethiopia, and China each has more than 1 million unvaccinated infants.
In the United States, routine measles vaccination is recommended at age 12-15 months. Children typically receive a booster at age 4-6. In this current climate of frequent importation from abroad, the Advisory Committee on Immunization Practices recommends that infants traveling internationally receive one dose of the vaccine at age 6-11 months. People born in 1957 through the 1960s may not be immune to measles, depending on the type of vaccine they received. According to the CDC, people who were vaccinated for measles during 1963-1967 received an inactivated (killed) vaccine that was not effective in producing long-lasting immunity.
Associated Press. Measles Outbreak Hits Europe, Especially France. http://healthland.time.com/2011/04/22/measles-outbreak-hits-europe-especially-france/
BBC News, World Edition. MMR’s Global Success. http://news.bbc.co.uk/2/hi/health/1804509.stm
Centers for Disease Control and Prevention. Measles Imported by Returning U.S. Travelers Aged 6-23 Months, 2001-2011. April 8, 2011 / 60(13);397-400. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6013a1.htm
Centers for Disease Control and Prevention. Measles – Q&A about Disease & Vaccine. http://www.cdc.gov/vaccines/vpd-vac/measles/faqs-dis-vac-risks.htm
Centers for Disease Control and Prevention. Measles—United States, January—May 20, 2011. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6020a7.htm
Centers for Disease Control and Prevention. Summary of Notifiable Diseases, 2009. May 13, 2011 / 58(53);1-100. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6018md.htm?s_cid=mm6018md_w
Minnesota Department of Health. Measles Update 4/27/2011. http://www.health.state.mn.us/divs/idepc/diseases/measles/
The World Health Organization. Immunization surveillance, assessment and monitoring: Measles. http://www.who.int/immunization_monitoring/diseases/measles/en/index.html