At the beginning of year, as measles rapidly spread among people who had recently visited Disneyland, health officials suspected the outbreak may have been linked to pockets of people who refuse vaccinations. Now, a new study provides some evidence to back up that theory.
Measles is highly contagious. Since it can spread so easily, moving through the air when an infected person coughs or sneezes, one person who has it can potentially put thousands of other people at risk. In order for a population to achieve “herd immunity,” which means it’s considered to be well-protected against measles, more than 95 percent of people need to receive the MMR vaccine that prevents them from contracting the infectious disease.
But, according to the new research published in JAMA Pediatrics, the people who were infected in the recent measles outbreak have vaccination rates that fall well below that recommended threshold. The researchers estimated that the rate could not have been higher than about 86 percent, and may have been as low as 50 percent.
“Clearly, MMR vaccination rates in many of the communities that have been affected by this outbreak fall well below the necessary threshold to sustain herd immunity, thus placing the greater population at risk as well,” the researchers concluded.
The “patient zero” in the Disneyland measles outbreak, which led to nearly 200 infections over the past three months, has not yet been confirmed. Federal officials suspect that a foreign visitor to the theme park brought the disease from overseas. Then, measles was able to spread quickly among clusters of families who have rejected the government’s immunization schedule for their children.
“The Disneyland outbreak is quite possibly a direct consequence of the growing anti-vaccination movement in the United States,” Maimuna Majumder, a research fellow at Boston Children’s Hospital and one of the authors of the new JAMA study, told HealthDay. She added that if that movement continues to grow, “the likelihood of outbreaks will increase — as will their scale and scope.”
Majumder explained that while experts have speculated that the recent spread of measles was due to low vaccine rates, her study “confirms this suspicion in a scientifically rigorous way.” Other infectious disease experts who were not involved in the research agree, and have expressed some fears about the troubling implications of her findings.
“A level of protection against measles as low as 50 percent makes pediatricians, infectious-disease experts, and the public health community profoundly concerned,” Dr. William Schaffner, a professor of infectious diseases at the Vanderbilt University School of Medicine, told Live Science.
While the JAMA study is the first to definitively link vaccine refusal to the most recent measles outbreak, previous studies have documented a similar trend on a larger scale. Across the country, federal health officials have tracked a rise in the number of measles cases that they say are driven by a fewer number of people getting the MMR shot. Although the national rates of MMR vaccination are around 92 percent, recent research has found that unvaccinated people tend to cluster together in the same community, which allows contagious diseases to more easily spread. Some school districts in Colorado, for example, have undervaccination rates five times higher than the state average.
It’s rare for Americans to reject every single recommended childhood vaccine. According to one 2009 study published in the New England Journal of Medicine, just two percent of the population refuses vaccines altogether.
Nonetheless, anti-vaccine beliefs are still finding a way to take hold. A large portion of vaccine skeptical parents are opting to delay vaccines, spacing out their kids’ shots based on the misguided belief that it’s harmful for children to get too many shots at once. That can leave their children unprotected for longer than they would have been otherwise — potentially exposing them to diseases like measles, even if their parents are planning on eventually giving them the MMR shot.