Children who were not vaccinated against whooping cough were 23 times more likely to catch the illness, according to a U.S. study.

The illness, known as pertussis, is a highly contagious bacterial disease that causes uncontrollable, violent coughing and can be deadly in infants.

'This study helps dispel one of the commonly held beliefs among vaccine-refusing parents: that their children are not at risk for vaccine preventable diseases.'— researcher Jason Glanz

In Tuesday's online issue of the journal Pediatrics, researchers looked at 751 children enrolled in a health plan in Colorado between 1996 and 2007, including 156 who got whopping cough, according to their medical records.

Among children with whooping cough, 18, or 12 per cent, had parents who refused the vaccine, compared with three or 0.5 per cent in a comparison group of 595 children who didn't get sick and included children who had at least some of the recommended series of five doses.

"This study helps dispel one of the commonly held beliefs among vaccine-refusing parents: that their children are not at risk for vaccine preventable diseases," the study's lead author, Jason Glanz — a senior scientist at Kaiser Permanente Colorado's Institute for Health Research in Denver — said in a release.

Community level protection

Based on the findings, one in 10 additional whooping cough infections could have been prevented by immunization, Glanz added.

Parents who assume "herd immunity" from others who vaccinate their children will offer protection for everyone may be mistaken when immunization rates drop too low.

"Herd immunity does not seem to completely protect unvaccinated children from pertussis," the researchers concluded in the study.

"These findings stress the need to further understand why parents refuse immunizations and to develop strategies for conveying the risks and benefits of immunizations to parents more effectively."

Childhood vaccinations for whooping cough are given in five doses between two months and 18 months of age.

Last month, infectious-disease experts said Canada is making strides against whooping cough in adolescents but needs to do more to prevent the illness in adults.

Health officials across North America have seen a resurgence in whooping cough among adolescents and adults since the 1990s, likely due to waning immunity, poor effectiveness of a previous vaccine and increased diagnosis.

With files from The Canadian Press