continued The new study is based on 40,810 adult travelers who each visited one of 24 Global TravEpiNet clinic sites, affiliated with a hospital, medical school, doctor's office, pharmacy or public health clinic, in the US between 2009 and 2014.
Of those travelers, 6,612 were eligible for MMR vaccine at the time of their visit, before they went abroad. However, 3,477 -- or 53% -- ended up not getting vaccinated, the data revealed.
"We were surprised to see such a high number of missed opportunities for MMR vaccination, even in these specialized travel clinics," Hyle said.
"To my knowledge, our study presents the largest analysis of systematically collected data about pre-travel MMR vaccination," she said. "Providers should have clear discussions with their patients about the potential risks of having measles illness and the risks of spreading the disease upon return to the US, especially to the very young and the immunosuppressed."
People with certain health conditions and children under 6 months old should not be vaccinated, Hyle said.
After analyzing questionnaires taken during each traveler's visit, the researchers found that 48% of those who were not vaccinated -- despite being eligible because they had not received it before -- refused the vaccination, as most thought it was unnecessary. Among 28%, the provider deemed the vaccine to be unnecessary, and for the remaining 24%, there were barriers to getting vaccinated, such as the patient being referred to another provider for the vaccine and never going.
"People often underestimate the risk of getting infections," said Dr. Pritish Tosh, an infectious disease physician and researcher at the Mayo Clinic in Rochester, Minnesota, who was not involved in the new paper.
The highest-risk group for travel-related illnesses tends to be people who think they are at a lower risk, Tosh said.
For instance, "people who were from a country and come to the United States to live and then they visit their friends and relatives back in their country of origin and they often think, 'Well, when I was there, things were fine,' and they don't seek travel advice. They don't get medications to prevent malaria. They don't get vaccinations and these other things," he said. "So, the people who think they are the lowest risk actually have the highest risk of getting some sort of travel-related infection, mostly because they don't think they are at risk."
Hyle said more research is needed to determine whether the new study findings might be generalizable to other health clinics and travelers.
"Additionally, travelers who seek pre-travel medical advice may be more likely to be up-to-date on their vaccines and might be more likely to accept vaccination than travelers who do not seek pre-travel advice; as a result, our findings might underestimate opportunities for MMR vaccination among travelers," she said.
Your guide to travel vaccinations, by country
Measles isn't the only vaccine-related health issue flagged under the CDC's travel notices.
"Hepatitis A is a potential risk almost anywhere in the world, so this vaccine is recommended for almost all international travelers," said the CDC's Kozarsky.