Gaps in measles vaccination rates place one in eight children at risk for becoming sick from the highly contagious illness, a new study says.

Measles is one of the most contagious of the vaccine-preventable diseases, meaning it's necessary to maintain the highest levels of immunity to prevent transmission. Once a common childhood ailment, health officials say it is sometimes not viewed seriously enough, noting that the disease can lead to pneumonia, encephalitis, hospitalization and occasionally, death.

According to Emory University researchers, their study suggests that nearly nine million children - infants through 17 - are susceptible to measles primarily because they haven't received the measles, mumps and rubella (MMR) vaccine, or have received only one of the two recommended doses.

They also found that nearly one in four children aged three or younger are at risk, and that nearly five percent of 17-year-olds had not received any doses of the vaccine.

A highly contagious disease, measles was generally eliminated 15 years ago, thanks to the vaccine, but coverage gaps have occurred mostly because some parents are reluctant to vaccinate their children, or delay it, opting out for religious or personal reasons, the study said.

Since last year, there have been 789 cases of measles reported, largely related to a multi-state outbreak that originated in Disneyland and has since subsided, according to the latest Centers for Disease Control statistics.