Update: Measles -- United States, January-July 2008

MA Grigg; AL Brzezny, MD; J Dawson, PhD; K Rietberg, MPH; C DeBolt, MPH; P Linchangco, MPH; S Smith, MPH; S Jones, M Vernon, DrPH; C Counard, MD; R Chugh, MD; S Nelson, MPH; K Green; C Petit; J Vercillo; S Cesario; K Hunt; C Conover, MD; J Daniels, K McMahon; SB Redd; KM Gallagher, DSc; GL Armstrong, MD; LJ Anderson, MD; JF Seward, MBBS; PA Rota, PhD; JS Rota, MPH; L Lowe, MS; WJ Bellini, PhD

Disclosures

Morbidity and Mortality Weekly Report. 2008;57(33):893-896. 

In This Article

Editorial Note

The number of measles cases reported during January 1--July 31, 2008, is the highest year-to-date since 1996. This increase was not the result of a greater number of imported cases, but was the result of greater viral transmission after importation into the United States, leading to a greater number of importation-associated cases. These importation-associated cases have occurred largely among school-aged children who were eligible for vaccination but whose parents chose not to have them vaccinated. One study has suggested an increasing number of vaccine exemptions among children who attend school in states that allow philosophical exemptions.[6] In addition, home-schooled children are not covered by school-entry vaccination requirements in many states. The increase in importation-associated cases this year is a concern and might herald a larger increase in measles morbidity, especially in communities with many unvaccinated residents.

In the United States, measles caused 450 reported deaths and 4,000 cases of encephalitis annually before measles vaccine became available in the mid-1960s.[1] Through a successful measles vaccination program, the United States eliminated endemic measles transmission.[1] Sustaining elimination requires maintaining high MMR vaccine coverage rates, particularly among preschool (>90% 1-dose coverage) and school-aged children (>95% 2-dose coverage).[7] High coverage levels provide herd immunity, decreasing everyone's risk for measles exposure and affording protection to persons who cannot be vaccinated. However, herd immunity does not provide 100% protection, especially in communities with large numbers of unvaccinated persons. For the foreseeable future, measles importations into the United States will continue to occur because measles is still common in Europe and other regions of the world. Within the United States, the current national MMR vaccine coverage rate is adequate to prevent the sustained spread of measles. However, importations of measles likely will continue to cause outbreaks in communities that have sizeable clusters of unvaccinated persons.

Measles is one of the first diseases to reappear when vaccination coverage rates fall. Ongoing outbreaks are occurring in European countries where rates of vaccination coverage are lower than those in the United States, including Austria, Italy, and Switzerland.[3,4] In June 2008, the United Kingdom's Health Protection Agency declared that, because of a drop in vaccination coverage levels (to 80%--85% among children aged 2 years), measles was again endemic in the United Kingdom,[3,8] 14 years after it had been eliminated. Since April 2008, two measles-related deaths have been reported in Europe, both in children ineligible to receive MMR vaccine because of congenital immunologic compromise.[4,8] Such children depend on herd immunity for protection from the disease, as do children aged <12 months, who normally are too young to receive the vaccine. Otherwise healthy children with measles also are at risk for severe complications, including encephalitis and pneumonia, which can lead to permanent disability or death.

The measles outbreaks in Illinois and Washington demonstrate that measles remains a risk for unvaccinated persons and those who come in contact with them.[9,10] Each school year, parents should ensure that their children's vaccinations are current, regardless of whether the children are returning to school, attending day care, or being schooled at home. Adults without evidence of measles immunity should receive at least 1 dose of MMR vaccine. All persons who travel internationally also should be up-to-date on their measles vaccination and other vaccinations recommended for countries they might visit. These recommendations include a single dose of MMR vaccine for infant travelers aged 6--11 months and 2 doses, administered at least 28 days apart, for children aged ≥12 months.[5]

Documented receipt of 2 doses of live measles virus vaccine, laboratory evidence of immunity, documentation of physician-diagnosed measles, or birth before 1957.

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