Importation of Vaccine-Preventable Diseases
Abstract & Commentary
By Corryn S. Greenwood, MD, and Philip R. Fischer, MD, Dr. Greenwood is a resident in the Department of Pediatric and Adolescent Medicine at the Mayo Clinic in Rochester, MN. Dr. Fischer is a Professor of Pediatrics, Division of General Pediatrics and Adolescent Medicine, Mayo Clinic, Rochester, MN.
Dr. Greenwood and Dr. Fischer report no financial relationships related to this field of study.
This article originally appeared in the June 2008 issue of Travel Medicine Advisor. It was edited by Frank Bia, MD, and peer reviewed by Phillip Fischer, MD, DTM&H. Dr. Bia is Professor of Medicine and Laboratory medicine; Co-Director, Tropical Medicine and International Travelers' Clinic, Yale University School of Medicine, and Dr. Fischer is Professor of Pediatrics, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN. Dr. Bia is a consultant for Pfizer and Sanofi Pasteur, and receives funds from Johnson & Johnson, and Dr. Fischer reports no financial relationships relevant to this field of study.
Synopsis: Recent reports of imported measles and mumps serve as reminders that all travelers should be fully current with routine childhood immunizations.
Sources: Takahashi H, Saito H. Measles exportation from Japan to the United States, 1994 to 2006. J Travel Med 2008;15:82-86; Dayan GH, et al. Recent resurgence of mumps in the United States. N Engl J Med 2008;358:1580-1589; Polgreen PM, et al. The duration of mumps virus shedding after the onset of symptoms. Clin Infect Dis 2008;46:1447-1449.
Over the past several years, Japan has been the chief source of measles importation into the United States. A total of 63 cases of measles were imported to the United States from Japan during the past 22 years. Individuals of almost all age groups were affected (median 17 years, range 9 months-53 years). Ninety percent of such cases occurred in citizens of Japan, and cases identified in the United States reflected common destinations of Japanese visitors (27 in Hawaii, 15 in California, and six in New York). Seven of the infected individuals were known to have transmitted measles to other people in the United States, one of them initiating an outbreak that involved 33 high school students in Alaska. The majority of subjects with known vaccine histories had not been vaccinated against measles.
The largest US outbreak of mumps in the past two decades occurred in 2006 when there were 6,584 cases. A total of 85 subjects were hospitalized, but no fatal cases were identified. Eighty-five percent of cases occurred in eight contiguous Midwestern states, and cases were often associated with outbreaks on college campuses. Orchitis was the most common complication. Sixty-three percent of infected patients overall (and 84% of those aged 18 to 24 years) had received two doses of mumps vaccine. Interestingly, the main mumps virus genotype, G, was identical to the strain isolated from the 2004-2006 outbreak in the United Kingdom that affected more than 70,000 individuals.
Post-outbreak analysis suggests that 8%-15% of mumps patients were still shedding virus more than five days after the onset of symptoms. The new data suggest that infected patients should be isolated for nine days after the onset of symptoms rather than the currently recommended five days.
Commentary
It's summer time. Children, adolescents, and young adults are flying around the world for vacations. Microbes, too, are being flown around the world.
Already this year, there have been measles outbreaks in Wisconsin, Arizona (apparently imported from Switzerland), Virginia (from India), and New York (from Israel).1 Several lessons from these outbreaks are relevant to travel medicine practitioners.
Imported measles is not simply originating from developing countries. In fact, trips to Japan, Switzerland, and Israel (or the United Kingdom, as seen with the mumps outbreak) rarely prompt pre-travel consultations. All physicians should seek to ensure that all their patients, traveling or not, are current on "routine" vaccines against childhood illnesses. What, however, constitutes "current?" In the United States, it is recommended that everyone born after 1956 have two measles-mumps-rubella vaccines. (Older individuals are thought to have high likelihood of having had natural immunity from illness exposure in the pre-vaccine era.) In Canada, it is birth after 1970 that prompts the recommendation of two measles-mumps-rubella vaccines. For pre-travel consultations, illness visits, and health maintenance visits, the recent outbreaks provide fresh reminders for physicians to emphasize the need for compliance with routine vaccination schedules.
The mumps outbreak, however, reminds us that even compliance with vaccination recommendations does not fully protect patients. The vaccines are expected to be 95% effective, but this still leaves a significant number of at-risk individuals who are especially susceptible when in close quarters in college dormitories and classrooms. Isolation recommendations have been modified to help protect non-immune individuals from exposure to patients who might still be shedding infective virus more than a week after the onset of illness. Concern about vaccine failures has also stimulated discussion of developing improved vaccines against the recently common virus genotypes.
Vaccine recommendations, especially for children and adolescents, change frequently. Medical practitioners should consult up-to-date sources2 as they seek to keep all travelers up-to-date on all routine vaccines. With hepatitis A vaccine and meningococcal vaccine now routine immunizations on childhood schedules, vaccines once considered to be unique to the practice of travel medicine currently are used broadly. Nonetheless, adolescent travelers might not have received these vaccines, since the vaccines were not "routine" at the time present-day adolescents were young children. New routinely scheduled vaccines, such as the one against human papillomavirus, can also be given prior to international trips when the traveler has not yet been vaccinated and when there is risk of transmission.
Several of the patients in the mumps outbreak were younger than the 12-month age at which the measles-mumps-rubella vaccine is usually given. When infants are traveling and might incur increased risk of vaccine-preventable diseases, "accelerated" schedules may be used. Levels of trans-placentally acquired maternal anti-bodies are waning between six and 12 months of age. Measles-mumps-rubella vaccine, for example, may be given during the first year of life, especially after six months of age, when the risk of disease is felt to outweigh the cost and inconvenience of vaccination. Potential "accelerations" in vaccine scheduling are available in the published literature.3
References
- International Society for Infectious Diseases. ProMed, April 13, 2008 (www.promedmail.org).
- Centers for Disease Control and Prevention web site. Immunization schedules. http://www.cdc.gov/vaccines. Accessed May 12, 2008.
- Centers for Disease Control and Prevention web site. Chapter 8: International Travel with Infants and Young Children. Travelers' Health Yellow Book. http://wwwn.cdc.gov/travel. Accessed May 12, 2008.
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