Researchers have identified a list of metropolitan areas in the US where low vaccination rates could lead to outbreaks of preventable diseases like mumps, whooping cough, measles, and more.
In the study, published in the journal PLOS Medicine, researchers looked at the rates of nonmedical exemptions (NMEs) for vaccines among kindergarten-aged children in the 18 states that allow NMEs. That means states where parents can decline vaccines for their children based on philosophical or religious beliefs, even though there's no medical reason not to vaccinate.
The data show that the NME rates have been on the rise in 12 of those 18 states since 2009, and in those areas, fewer children received vaccines such as MMR, which protects against measles, mumps, and rubella.
Looking at that data county by county, the researchers identified several hot spots where high prevalence of NMEs were clustered, including Seattle and Spokane in Washington; Phoenix; Salt Lake City and Provo in Utah; Houston, Austin, Fort Worth, and Plano in Texas; and Troy, Warren, and Detroit in Michigan. There were also rural areas of concern, such as in Idaho, and other areas like Portland, Oregon; Kansas City, Missouri; and Pittsburgh. The researchers are now looking into why these areas have high NME rates.
"These NMEs are in fact harming the public health in those 18 states," said Peter J. Hotez, dean of the National School of Tropical Medicine at the Baylor College of Medicine in Houston, and one of the authors of the study.
His concern, he told BuzzFeed News, is that vaccination rates will drop enough that herd immunity is compromised, leading to outbreaks of potentially deadly but preventable diseases.
Herd immunity means enough people in the population are vaccinated against a disease that if the disease appears, its spread is limited. Hotez said for measles, for example, 90%–95% of the population needs to be vaccinated for herd immunity to work.
"Once you start dipping below that you're always at risk, and that's what happened in California, in Minnesota," said Hotez.
In December 2014, 40 people who either worked at or had visited Disneyland in Anaheim, California, came down with measles. By the end of the outbreak the following April, 159 people across 18 states had contracted the disease, with most of those tied back to the original Disneyland outbreak. The vaccination rate was 50%–86% in the city, compared with 72% across the US in general. The case led California to ban nonmedical exemptions for school vaccines.
More recently, in Minnesota, a measles outbreak infected 78 people in 2017, the majority of whom were not vaccinated.
"This is a self-inflicted wound," said Hotez. "We can do something about this by closing NMEs."
Peter J. Hotez is dean of the National School of Tropical Medicine at the Baylor College of Medicine in Houston, not Baylor University.