The number of unvaccinated people exposed to the measles at Disneyland might have been even greater than public health officials had previously thought, according to new research.
As little as 50 percent of people exposed at Disneyland had been vaccinated, according to a study published Monday by JAMA Pediatrics. The Disneyland outbreak has infected dozens of people in the last four months, a trend that has alarmed public health officials nationally.
A total of 173 people have been infected with the measles so far this year, and many of the cases can be linked to Disneyland, according to the Centers for Disease Control and Prevention (CDC).
Low vaccination rates are "likely to blame" for the outbreak, according to researchers from institutions like the Massachusetts Institute of Technology.
A vaccination rate below 96 percent in any community is considered unsafe, because infections are more likely to spread in communities that do not achieve "herd immunity." The researchers warned that low vaccination rates not only increases the likelihood of an individual becoming infected, but also places "the greater population at risk" as well.
Health officials had warned that vaccine refusal had been a major factor in the recent outbreaks, but the new study provides the most comprehensive look to date about the people who helped spread the outbreak.
"Disneyland is an international attraction and sometimes people are coming from places where measles vaccination rates are low or they don't get the recommended two doses, and that, combined with the fact that there are a lot of pockets of non-vaccination in California and people coming from all over the U.S. created the perfect storm for a big outbreak," the study's lead author, Maimuna Majumder, told Reuters.
The rate of vaccination could have been as high as 86 percent, though researchers said that even that figure falls "well below" the 96 percent rate that is considered safe for public health.
The researchers also determined that the outbreak first began spreading between Dec. 17 and Dec. 20 last year.