By Mary Elizabeth Dallas
"Instead of having an 18 percent risk of treatment failure, with flu their risk rises to 40 percent," said Ducharme, a professor at the University of Montreal.
Asthma is a chronic disease of the airways.
"These kids should get their flu shot and they should get it systematically -- it's worth it," Ducharme said in a university news release.
For the study, the researchers examined roughly 1,000 children treated for moderate or severe asthma attacks in emergency rooms at five Canadian hospitals. They also analyzed nose swabs taken from the kids to determine if they also had the flu or another respiratory virus.
Nearly two-thirds tested positive for a viral infection. But when given the standard treatments for an asthma attack -- including oral corticosteroids and inhaled bronchodilators -- 19 percent didn't respond to their medications.
Those with influenza or parainfluenza turned out to have a 37 percent higher chance of not responding to treatment, compared to 13 percent for children without the virus.
Asthma treatment was also more likely to fail among children with respiratory syncytial virus (RSV), the study showed. But human rhinoviruses -- the usual cause of common colds -- did not reduce the effectiveness of asthma treatment, the study authors said.
The authors added that the flu shot is a simple way people with asthma can protect against dangerous flu-related complications.
"Influenza is the only respiratory virus that is vaccine-preventable. Granted, it's at best only 50 percent efficacious, but that's no reason for kids with asthma not to get vaccinated yearly, in the fall, before flu season starts," said co-author Caroline Quach, an associate professor of microbiology and infectious diseases at the University of Montreal.
The study was published June 4 in the journal Pediatrics.