A new study published by The Lancet Infectious Diseases, a prominent medical journal, lists Maricopa County as one of the U.S. counties most likely to experience a measles outbreak.
The study, produced by the team of researchers that in 2015 correctly predicted where the Zika outbreak would strike, ranked Maricopa County No. 6, behind two counties – Queens in New York and King in Washington – that have already had measles outbreaks this year.
The researchers looked at population size, rates of non-medical exemptions from vaccination and incoming international air travel volume.
“The seriousness of this risk is underscored by the ease of transmission of measles, which is caused by the highly contagious measles morbillivirus that is capable of airborne spread,” the researchers wrote.
In Arizona, there has been a spike in the number of parents opting not to vaccinate their kids in recent years.
All 25 of the counties identified as having high risks of outbreaks either contain an international airport or are adjacent to a county with an international airport. Studies have shown that measles outbreaks in the U.S. are usually sparked by travel to or from a foreign country, where vaccination rates are much lower.
Although Maricopa County was the only Arizona county included in the report, it is actually in the middle of the pack for vaccination rates among Arizona’s 15 counties, according to data from the Arizona Department of Health Services, with 92.7 percent of kindergartners in the current school year having received the measles vaccine.
By comparison, only 83.3 percent of kindergartners in Yavapai County have been vaccinated for measles. Yuma County had the highest vaccination rate, at 97.3 percent.
Scientists and health advocates say that communities in which at least 95 percent of people are vaccinated against a disease have achieved herd immunity, which means that infectious diseases are unable to widely spread.
Arizona law gives wide latitude to parents to exempt their children from vaccines for “personal beliefs,” and ADHS collects data on those non-medical exemptions. Yavapai County again leads the state in personal-belief exemptions, with 12.5 percent of kindergartners this year receiving an exemption from at least one of the required vaccines because of a family’s beliefs. In all, 7.7 percent of kindergartners in that county were exempted from receiving any vaccine.
In Maricopa County, 6.5 percent of kindergartners this school year received personal-belief exemptions. The state’s other populous urban county, Pima, saw fewer than half that many, with only 3.2 percent receiving exemptions.
Yuma and Greenlee counties had the lowest exemption rate, at 1.3 percent.