Nonmedical exemptions to vaccines are on the rise in many of the states that allow them, which is creating pockets of vulnerability across the United States, according to new research.
Researchers examined the rate of philosophical belief nonmedical exemptions (NMEs) in 18 states that currently allow these type of exemptions in a study published in PLOS Medicine. They found that the rates of NMEs had increased in 12 of these states since 2009.
"There are pockets in the United States where vaccine NMEs are widespread and there is risk of breakthrough infections," coauthor Peter Hotez, MD, PhD, FAAP, dean of the National School of Tropical Medicine at Baylor College of Medicine, Houston, tells Drug Topics.
The researchers also identified what they called "hotspot" areas where there are large numbers of NMEs.
These areas were identified as: Seattle; Spokane, WA; Portland, OR; Phoenix; Salt Lake City; Provo, UT; Houston; Fort Worth; Plano, TX; Austin, TX; Troy, MI; Warren, MI; Detroit; Kansas City, MO; and Pittsburgh.
"Especially in some of the western state counties there are large numbers of children not receiving their routine vaccinations," Hotez said.
As the rate of NMEs increases, he said, it can create risks for breakthrough childhood infectious diseases. The risk for measles is particularly significant because it's so highly transmissible.
Researchers don't know why the rates have been rising in recent years in those dozen states. While researchers found that, in some of the states identified, the rates appear to have plateaued in the last few years, rates in at least a third of the 18 states that allow exemptions continue to be on the rise.
"We're concerned that in several states, it's the result of organized antivaccine activities," Hotez said, adding that more research is needed to better understand why this is happening, and whether there are common social or demographic factors in areas with high NMEs.
The authors of the study also examined whether the rate of NMEs corresponded with actual vaccination coverage. They reported there was an inverse association between the NME rate and number of kindergarten students who were vaccinated for measles, mumps, and rubella.
Researchers believe the findings could also have implications for other countries who either allow NMEs or are considering them.
"Our concern is that the rising NMEs linked to the antivaccine movement in the US will stimulate other countries to follow a similar path," they wrote in the study.