Measles: Travel, Lack of Vaccination Root of US Outbreaks

Neil Osterweil

April 16, 2015

Most of the measles cases reported in the United States in the first 3 months of 2015 can be traced to people who were either not vaccinated against the highly contagious virus or had unknown vaccination status, according to the Centers for Disease Control and Prevention (CDC).

There were four measles outbreaks in the United States from January 4 through April 2, 2015, with one outbreak, linked to Disney's California theme parks, accounting for 70% of all measles cases. A total of 159 people, including 155 US residents and four foreign visitors, were affected. Eighteen states and the District of Columbia have reported cases.

Twenty-two patients have been hospitalized, including five because of pneumonia.

In all, 68 US residents who developed measles had not received the measles, mumps, and rubella (MMR) or other vaccine against the measles virus. Of this group, 29 said they had religious or philosophical objections to vaccination, 26 were too young to be vaccinated, and one had a medical contraindication. The remaining 12 people had either missed the opportunity to be vaccinated or had other, unspecified reasons.

"Maintenance of high 2-dose MMR vaccine coverage has been crucial in limiting measles spread from importations in the United States. Most measles importations occur when U.S. citizens travel abroad and have not been appropriately vaccinated. Therefore, it is important to encourage timely delivery of measles vaccination for U.S. residents before overseas travel," write Nakia S. Clemmons, MPH, from the Division of Viral Diseases, National Center for Immunization and Respiratory Disease, CDC, and colleagues in an article published in the April 17 issue of the Morbidity and Mortality and Weekly Report.

All but six of the cases this year have been linked to importation of infections from countries in which measles remains endemic.

Investigators classified 10 cases as "direct importation," including six unvaccinated US residents returning from overseas travel and four foreign visitors. Countries associated with direct importations (one case each) included Azerbaijan, China, Germany, India, Indonesia, Kyrgyzstan, Pakistan, Qatar, Singapore, and the United Arab Emirates.

The CDC recommends that healthcare providers encourage vaccination of all eligible persons who are not known to have measles immunity.

"Children without contraindications should receive their first dose of [MMR] vaccine at age 12–15 months and a second dose at age 4–6 years. Before international travel, infants aged 6-11 months should receive one dose of MMR and children aged 12 months and older should receive two doses of MMR vaccine separated by at least 28 days," the authors write.

Adults born in 1957 or later who are at high risk for measles because of potential occupational exposures or international travel, and who do not have other evidence of measles immunity, should also be given two doses of the MMR vaccine, they add.

Morb Mortal Wkly Rep. 2015;64:373-376. Full text

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