Dr. Adrienne Randolph of Children's Hospital Boston, the study leader, said during the 2009 H1N1 influenza pandemic, many previously healthy children became critically ill, developing severe pneumonia and respiratory failure, and some died.
The study, published in the journal Pediatrics, found having H1N1 and MRSA simultaneously increased the risk for flu-related mortality eightfold among previously healthy children.
Moreover, almost all of these co-infected children died despite being treated quickly with vancomycin.
"There's more risk for MRSA to become invasive in the presence of flu or other viruses," Randolph said in a statement. "These deaths in co-infected children are a warning sign."
The researchers said the findings make clear why flu vaccination among all children age 6 months and older is imperative.
"The 2009 H1N1 virus has not changed significantly to date," said Dr. Tim Uyeki of the Influenza Division of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention in Atlanta who was the lead investigator.
"Infections of children in the U.S. with 2009 H1N1 virus are expected this season and need to be prevented and treated appropriately. Influenza vaccination protects against 2009 H1N1 illness."