US Measles Outbreaks Often Begin Overseas

Neil Osterweil

September 12, 2013

Nearly all cases of measles reported in the United States since January 2013 were imported, and most occurred in people who were either unvaccinated or had uncertain measles vaccine histories, according to an article published in the September 13 issue of the Morbidity and Mortality Weekly Report.

Of the 159 cases of measles reported by 16 states and New York City from January 1 through August 24, 2013, all but 2 (99%) were "import-associated," note Carla L. Black, PhD, from the Immunization Services Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention and colleagues. Furthermore, 91% of the cases were in people who had not been vaccinated (82%) or whose vaccination status was unknown (9%).

Of the 159 cases reported in 2013, 140 were in US residents, 84% of whom had not been vaccinated against measles and 8% of whom had unknown vaccination status. Most of the unvaccinated cases (79%) had philosophical objections to vaccination, 6 (5%) had missed the chance to get vaccinated, 15 (13%) were infants younger than 1 year of age who were not eligible for measles shots, and 4 (4%) were unvaccinated for unknown reasons.

Three regions (New York City, North Carolina, and Texas) had outbreaks that accounted for 77% of all measles cases reported in the United States through August 24. Of the 58 cases in New York, 67% of the unimmunized individuals who were eligible for vaccination had philosophical or religious objections on the part of patients or the parents of patients.

"As these outbreaks are showing, clusters of people with like-minded beliefs leading them to forego vaccines can be susceptible to outbreaks when measles virus is imported from elsewhere," said Anne Schuchat, MD, director of the National Center for Immunization and Respiratory Diseases at the CDC, during a media briefing.

Most Vaccine Targets Met or Exceeded

However, as Dr. Schuchat noted, data from the most recent National Immunization Survey show that childhood immunization programs in the United States either meet or come to close to meeting target goals of 90% or greater coverage established by the Healthy People 2020 initiative.

In 2012, 90.8% of children had at least 1 dose of the measles, mumps, and rubella vaccine, 89.7% had 3 or more of the recommended doses of for hepatitis B vaccine, 92.8% received at least 3 recommended doses of poliovirus vaccine, and 90.2% got at least a single dose of the vaccine against the varicella virus.

There were small but statistically significant decreases from 2011 to 2012 in several vaccination categories, but these changes may have been a result of a change in statistical sampling methods from 1 year to the next; specifically, a 4-fold increase in the sample of households surveyed by cell phone rather than landline telephone. This change is expected to provide a much more accurate portrait of the US population as a whole going forward, Dr, Schuchat said.

Vaccination coverage also varied by state and tended to be lower among children living below the poverty level, she noted.

Asked by Medscape Medical News what practitioners can do to encourage vaccination of eligible patients, Dr. Schuchat said "virtually all parents want to keep their children healthy and safe, and we know that 99% of today's toddlers have received at least some vaccine."

She emphasized that a provider's recommendation is the strongest influence on parental decisions about child health.

"It's also important for clinicians to listen and to make sure they understand what concerns and questions parents have and that they address them and take them seriously," she said.

In addition, Medscape Medical News has reported previously on information clinicians can give to patients or parents of patients.

The reports were supported by the CDC. Dr. Schuchat and the authors of the childhood vaccine report are employees of the CDC and report having no other conflicts of interest.

Morb Mortal Wkly Rep. 2013;62;733-740. Full text

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