(This June 12 story updates “hotspot list” in paragraph 3 after researchers announced an error in their report; also adds new final paragraph.)

(Reuters Health) - A growing number of children are missing out on recommended vaccinations in states that permit parents to skip inoculations due to their personal beliefs even when there’s no medical reason kids can’t be vaccinated, a U.S. study suggests.

Eighteen U.S. states currently allow parents to opt out of vaccinations recommended for kindergarten if they have a philosophical or religious objection. Since 2009, the proportion of children missing recommended vaccinations has climbed in 12 of those states: Arkansas, Arizona, Idaho, Maine, Minnesota, Missouri, North Dakota, Ohio, Oklahoma, Oregon, Texas, and Utah, researchers report in PLOS Medicine.

In several of these states, there are “hot spots” with vaccine exemption rates too high to protect people in the community against highly contagious vaccine-preventable diseases like measles. Hot spots include several rural communities as well as cities like Detroit, Houston, Kansas City, Phoenix, Portland, Salt Lake City, Seattle and Tacoma, Washington.

“Vaccine exemptions for reasons of personal belief have caused a lot of damage in terms of facilitating breakthrough measles epidemics,” said study co-author Dr. Peter Hotez of Baylor College of Medicine in Houston.

“California, for instance, experienced a terrible measles outbreak in 2015 due to declines in vaccine coverage, while last year the Twin Cities suffered a prolonged measles outbreak among the Somali immigrant community,” Hotez said by email. “In both instances, vaccine coverage declined due to organized anti-vaccine movements alleging that vaccines cause autism and other illnesses, despite overwhelming scientific evidence that there is no link.”

While influenza cases often spike where vaccination rates are lower, measles cases often provide some of the first evidence of hotspots because each case typically leads to an average of 12 to 18 unvaccinated kids and adults catching measles, Hotez said.

Measles is a highly contagious virus that can be serious or even fatal. It starts with a fever that can last a couple of days, followed by a cough, runny nose and pink eye. A rash develops on the face and neck and then spreads to the rest of the body. In severe cases, pneumonia and encephalitis, an inflammation of the brain, can develop.

People with measles can be spreading the virus for four days before and after the rash appears, according to the Centers for Disease Control and Prevention.

The virus can live for up to two hours on surfaces where an infected person coughs or sneezes. People can become infected by breathing in droplets or touching a contaminated surface and then touching their eyes, nose or mouth.

At least 90 to 95 percent of people in the community need to be vaccinated against measles to provide what’s known as “herd immunity.” Herd immunity helps protects everyone in the community, including newborns, people with compromised immune systems and other individuals who can’t be vaccinated for medical reasons, researchers note.

For the current study, researchers examined routine public health data collected by states on the number of children enrolling in kindergarten with non-medical vaccine exemptions.

Eight of 10 counties with the highest rates of non-medical exemptions were in Idaho, primarily in rural areas, the study found.

Among urban areas, Phoenix had the highest non-medical exemption rate, followed by Salt Lake City, Seattle, and Portland.

Six states - Arizona, Idaho, Maine, Oregon, Utah, and Wisconsin - had non-medical exemption rates for the measles vaccine approaching or exceeding five percent, a point that can start to compromise herd immunity.

The study wasn’t a controlled experiment designed to prove whether or how non-medical exemptions might contribute to outbreaks of measles or other vaccine-preventable diseases.

Still, the results offer fresh evidence that state policies can contribute to lower vaccination rates, said Dr. Matthew Davis, a researcher at Northwestern University Feinberg School of Medicine in Chicago.

“Other studies had suggested that local communities with high numbers of unvaccinated children were susceptible to outbreaks of vaccine-preventable illnesses, such as measles and whooping cough,” Davis, who wasn’t involved in the study, said by email. “The current findings expand on prior research to illustrate how several states’ policies that allow non-medical exemptions correlate with lower rates of vaccination among children.”

The researchers’ June 12 report had originally included Pittsburgh in the list of hot spot cities, but on June 15 they corrected their calculations, removing Pittsburgh and adding Tacoma. “Quality control is very important to us and we regret that this data error was not picked up,” Hotez said in a press statement. “We are now implementing a double-data entry check system to prevent this from occurring in the future and appreciate that the Pennsylvania State Department of Health brought this to our attention.”

SOURCE: bit.ly/2l3z4Ap PLOS Medicine, online June 12, 2018.