The vast majority of measles cases occurring in the United States can be put down to Americans who have traveled abroad without being immunized against the disease.
Although measles has been officially eradicated in the United States since 2000, sporadic outbreaks continue to happen because unvaccinated people visiting foreign countries contract the disease elsewhere and bring back the virus upon returning home.
This puts their families and entire communities at risk of becoming infected, underlines a new study published May 16 in the journal Annals of Internal Medicine.
According to the paper, every year, millions of U.S. residents fly to foreign destinations without getting the measles, mumps, rubella (MMR) vaccine.
The reasons why these travelers skip the recommended measles jab are diverse, but in most instances, it all comes down to people's refusal to get vaccinated.
More Than Half Of US Travelers Bypass Measles Vaccination
The study, conducted by researchers at the Massachusetts General Hospital, aimed to get to the bottom of this situation and investigate both the process through which clinicians assess which travelers qualify for the measles vaccine and why some of the eligible people refuse vaccination.
The team analyzed data provided by 24 different travel clinics associated with the GlobalTravEpiNet (GTEN) consortium — a national network of clinics coordinated by Massachusetts General Hospital and funded by the Centers for Disease Control and Prevention.
The two dozens GTEN clinics provided information regarding 40,810 adults born after 1957 who were evaluated between 2009 and 2014.
Since the first measles vaccine didn't become available until the early 1960s, people born before 1957 are extremely likely to have had the disease and built immunity to the virus.
The general recommendations state that people who aren't immune to measles should receive two doses of the MMP vaccine before traveling abroad.
However, the study uncovered that more than half of U.S. travelers who should have been immunized didn't get vaccinated against measles before leaving the country.
The research revealed that although 6,612 people (16 percent of the cohort study) were eligible for vaccination, more than half of them — 53 percent, or 3,477 people — weren't vaccinated when they visited the travel clinic.
"Of U.S. adult travelers who presented for pretravel consultation at GTEN sites, 16 percent met criteria for MMR vaccination according to the provider's assessment, but fewer than half of these travelers were vaccinated," the authors write in the abstract of their paper.
Why Americans Traveling Abroad Aren't Getting the MMP Vaccine
The reasons why these nearly 3,500 people bypassed vaccination are as just as alarming as the potential consequences of this worrisome situation.
According to the research, 48 percent of them (or 1,689 people) simply refused getting the measles vaccine.
Data from the GTEN clinics pointed out three quarters of these travelers opted to skip vaccination because they weren't concerned about the measles, whereas about a fifth of them expressed concern about vaccine safety. The others mentioned cost as justification for denying immunization.
Another reason why half the people who qualified for the vaccine left the country without it has to do with the healthcare provider's decision not to administer it. The study further documented that 966 people (28 percent) weren't vaccinated because the provider thought they didn't need it.
Lastly, an additional 822 people (24 percent) didn't get the MMR vaccine due to health system barriers, such as the vaccine not being available at the clinic.
Study authors note that unvaccinated MMR-eligible travelers were more likely to have been evaluated in the South and at nonacademic health centers. It was also here that nonvaccination due to traveler refusal was most frequent — 1,432 people (63 percent) in the South and 1,178 people (66 percent) in nonacademic centers.
Why Measles Immunization Matters
Given that millions of U.S. residents fly to foreign countries each year, the study's results suggest that nearly 5 million of them could be at risk for measles.
"An increase in MMR vaccination of eligible U.S. adult travelers could reduce the likelihood of importation and transmission of measles virus," study authors show in their paper.
In a separate editorial related to the research, Dr. Lori Handy of Thomas Jefferson University and Dr. Paul Offit of the University of Pennsylvania pointed out, "exotic infections, such as malaria and yellow fever, preoccupy travelers," but "measles should be just as feared."
In their editorial, Handy and Offit remind the public that the 2014 measles outbreak that wreaked havoc in the United States was triggered by a combination of two factors: infected travelers importing the virus and the low vaccination rate of certain populations.
"This outbreak was linked to travel to the Philippines, which was in the midst of a measles epidemic. In 2015, a multistate outbreak associated with Disneyland likely was the result of a park visitor who had traveled overseas; 188 cases were reported that year," note the authors in their article, published on the same day as the Massachusetts General Hospital study.
Similarly, the current Minnesota measles outbreak, which — according to an update from the Minnesota Department of Health — has now reached 60 confirmed cases, is also associated with unvaccinated people in the Somali community living in Minneapolis. All but three of the outbreak patients were not vaccinated.
Handy and Offit advocate for strongly encouraging measles vaccination before flying abroad and believe the task to help educate travelers about the implications of the disease — its potential illness severity, contagiousness, and threat to the wider population — should fall on health providers.
Their view is also supported by lead study author Dr. Emily Hyle, who is an infectious disease specialist at Massachusetts General Hospital in Boston.
"It is a message that we hope will get out to all international travelers, even people who aren't considering their itineraries to be high-risk," she said in a statement.