The Resurgence of Measles: Guidance for Clinicians

Kristen A. Feemster, MD, MPH, MSHP

Disclosures

February 02, 2012

In This Article

Measles Today: A Public Health Threat

Measles is one of the most contagious infectious diseases in humans. It is a major contributor to child mortality worldwide and kills approximately 1-3 of every 1000 infected individuals, even in developed countries.[1] An effective vaccine was introduced in the 1960s, and along with global prioritization of measles control initiatives, this advance has significantly reduced the burden of disease. In 1997, 36 million cases and more than 1 million deaths occurred worldwide, but measles now accounts for an estimated 164,000 deaths per year globally. Endemic transmission was declared to be eliminated in the United States and the Americas in 2000.[2,3,4]

This was promising news, yet today, measles is reemerging as a public health threat. As of August 26, 2011, 198 cases and 15 outbreaks of measles were reported in the United States, the largest number of cases seen in this country since 1996.[5,6,7] In Europe, outbreaks have been ongoing in 36 of the 53 World Health Organization (WHO) European member countries, resulting in almost 30,000 cases in 2011. Measles is now considered endemic in the United Kingdom after being reportedly eliminated as of 1995.[8,9,10] In Africa, the number of cases increased from 36,000 in 2009 to 172,824 in 2010, and outbreaks were reported in countries with successful measles control programs.[3] Even in countries with widespread vaccine availability and a well-established public health infrastructure, sustaining measles control has become a growing challenge.

The Measles Revival

The reemergence of measles is the result of the confluence of 3 factors:

  • High transmissibility of the measles virus;

  • Increasing rates of vaccine refusal; and

  • Globalization.

Without vaccination, almost all susceptible individuals exposed to measles will become infected. Population vaccination rates of at least 90% are required to achieve herd immunity and disrupt sustained transmission.[3,4,11,12,13] Even in populations with high vaccination coverage, a group of unvaccinated susceptible individuals can reintroduce the virus in a community.[14,15] In the recent outbreaks in the United States, most cases occurred in unvaccinated persons.[5,6] Outbreaks have also been reported in older children and young adults with primary vaccine failure, especially before implementation of the 2-dose vaccine recommendation.[16,17,18,19,20]

Maintaining vaccine coverage according to current recommendations is paramount to ensuring population protection. However, vaccine refusal is increasingly contributing to clusters of intentionally unvaccinated individuals. Rates of vaccine refusal, especially in states that permit philosophical exemptions, are increasing, and recent data show significant geographic variation in coverage rates for the measles, mumps, and rubella vaccine (MMR).[21]Of 12 cases in a recent outbreak in California, 75% were children who were intentionally unvaccinated, and most of their parents reported vaccine safety concerns as the reason for vaccine refusal.[14]

Recent outbreaks also illustrate the effects of globalization. Measles remains endemic in many countries, including many European countries, making exposure a real possibility for susceptible travelers or visitors. In the United States, 89% of measles cases were imported by returning travelers or recent immigrants.[22,23,24]

The resurgence of measles puts those who cannot be vaccinated at risk, results in significant costs for outbreak investigations and containment activities, and could lead to a resurgence of measles-associated morbidity and mortality in children. Clinicians are at the forefront of recognizing and managing the disease, educating parents and guardians, and implementing vaccination recommendations amid growing concerns about vaccine safety.

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