Across the US, cases of chickenpox have dropped by about 80% since a vaccine to prevent the disease was made widely available early 15 years ago. But many parents still choose to reject immunization on the back of various safety concerns about the vaccine.

Now, a new study has revealed, once again, what health officials have been asserting for very long - children whose parents do not allow them to be immunized via the chickenpox vaccine are at an increased risk of contracting the disease.

133 children were identified by researchers from the Kaiser Permanente Institute for Health Research in Denver, out of some 90,000 children who had enrolled in a Colorado health plan. All the singled out children had contracted chickenpox, and they were compared with a total of 493 children "matched for sex, age, and length of enrollment in the health plan" who had not suffered from the disease.

It was then discovered that when parents refused the vaccine, children were 9 times more at risk of getting chickenpox.

"Many parents refuse the varicella vaccine because they think of chickenpox as a mild illness, but this is not necessarily true", study investigator Jason M. Glanz, PhD said.