More than half of adult travelers who were eligible to be vaccinated against measles during travel medicine clinic visits before their trips opted not to receive it, according to a new study that sheds new light on US vulnerability to imported measles cases.
Most measles infections in the United States can be traced to returning travelers who aren't protected against the disease, and the new findings about the gap in travelers comes amid a growing outbreak in Minnesota and a large outbreak in Europe that began in Romania last year and has spread to 14 other countries in the region.
The Minnesota outbreak has sickened 60 so far, mainly in unvaccinated people in the Somali population, according to an update today from the Minnesota Department of Health (MDH). All but 3 of the outbreak patients were not vaccinated.
A research team based at Massachusetts General Hospital reported the traveler vaccination findings yesterday in the Annals of Internal Medicine.
Reasons for vaccine declines
To get a glimpse of how clinicians assess for measles in travelers and why some of those who are eligible to receive the vaccine decline it, the team analyzed data on 40,810 people who were seen at 24 GlobalTravEpiNet clinics from 2009 to 2014. The clinics are part of a Centers for Disease Control and Prevention consortium.
People without evidence of measles immunity, through a blood test or documented measles infection, or those born before 1957 are recommended to receive two doses of measles, mumps, and rubella (MMR) vaccine before international travel.
The researchers found that 6,612 (16%) were eligible to receive the MMR vaccine, but 53% of them were not vaccinated at the travel clinic visit. Of the people who weren't vaccinated, 1,689 refused, with 74% of them saying they were not worried about the disease.
Worryingly, 966 (28%) weren't vaccinated because of the healthcare provider's decision, and 822 (24%) of those who didn't get the MMR vaccine reported health system barriers.
Unvaccinated MMR-eligible travelers were more likely to have been evaluated in the south and at nonacademic health centers.
The results point to the need for strategies to boost both patient and health provider knowledge of measles as a travel-related illness and the need to increase pre-travel MMR vaccine uptake, especially in communities that have higher proportions of people who aren't protected.
Key role for health providers
In an editorial on the study in the same Annals issue, Lori Handy, MD, and Paul Offit, MD, with the Children's Hospital of Philadelphia, reminded readers that an outbreak that sickened 188 people in the United States in 2015 was probably linked to a Disneyland visitor who traveled overseas and that visits to travel clinics offer an opportunity to reduce or eliminate clusters sparked by imported measles infections.
However, the experts noted that unvaccinated travelers are an overlooked population for increasing overall MMR immunization rates. Handy and Offit said that since people who visit travel clinics are probably interested in protecting themselves from diseases while traveling abroad, it's surprising that the MMR vaccination rates weren't higher. They added that the MMR immunization rates for those who don't or can't visits travel clinics may be even lower.
"Exotic infections, such as malaria and yellow fever, preoccupy travelers; measles should be just as feared, and vaccination should be strongly encouraged," they wrote.
The onus is on health providers to help educate travelers about the implications of measles—its potential illness severity, contagiousness, and treat to the wider population, according to Handy and Offit.
May 15 Ann Intern Med abstract
May 15 Ann Intern Med editorial
May 15 American College of Physicians press release
May 16 MDH measles update
May 12 European Centre for Disease Prevention and Control measles outbreak update