Parents born in certain countries are less likely than others to vaccinate their children, according to a study by the University of Washington School of Public Health.

The study, published online June 29 in Pediatrics, analyzed data on about 277,000 children living in Washington state. Almost a quarter of those studied had at least one parent born in Somalia, Ukraine, Russia, Mexico, or India.

To find out how a parent’s birthplace influenced childhood vaccination, researchers used birth records and the Washington State Immunization Information System. They looked at immunizations received by children aged 12 through 23 months, including measles-containing vaccines, hepatitis A, pneumococcal and diphtheria-tetanus-acellular pertussis (DTaP).

Children of Somali-born parents were 16 percent less likely to get a measles-containing vaccine than kids with parents born in the United States, the study found.

The study also noted that children of parents born in Ukraine and Russia were less likely to be vaccinated in general, while offspring of those born in Mexico and India were more likely to be immunized.

“Throughout the U.S., there is significant variation in immunization coverage,” said lead study author Elizabeth Wolf, now with Children’s Hospital of Richmond at Virginia Commonwealth University, as quoted by Reuters. “The phenomenon of clustering of unimmunized individuals has been associated with outbreaks of certain vaccine-preventable diseases such as whooping cough (pertussis) and measles.”

In 2011, for example, an outbreak of the measles in Minnesota was linked to low immunization of Somali children against measles, mumps and rubella (MMR), the study noted. Qualitative assessments within the Minnesota and Washington Somali communities found that MMR vaccine hesitancy was due to the belief that it causes autism.

To help prevent future outbreaks in Washington State, which is home to more than 943,000 immigrants, researchers suggest new and innovative forms of public health outreach is needed.

Washington is one of the top 10 states in the country for refugee resettlement, hosting the third largest population of Somali refugees in the U.S. Many more undocumented immigrants work in the state’s seasonal agricultural sector, the study noted.

The study was led by Wolf as part of her master’s degree in epidemiology for the School of Public Health. Other research partners include Ali Rowhani-Rahbar, assistant professor in the School’s department of epidemiology, as well as Azadeh Tasslimi, Jasmine Matheson, and Chas DeBolt from the Washington State Department of Health.