Older children more vulnerable to H1N1 influenza

A new research has shown that children hospitalised with pandemic H1N1 influenza in 2009 were older and more likely to have underlying medical conditions than children hospitalised with seasonal influenza during prior flu seasons.

The study is being presented at the Paediatric Academic Societies (PAS) annual meeting in Vancouver, British Columbia, Canada.

Population-based surveillance of 5.3 million children for laboratory-confirmed influenza was conducted in 10 states during the 2003-2009 influenza seasons and in the early 2009 H1N1 pandemic.

Researchers used the data to compare the demographics, medical history and clinical course of children younger than 18 years who were hospitalized with seasonal influenza vs. those hospitalised with H1N1 flu.

They found that the median age of children hospitalised with H1N1 influenza was five years, compared to one year for those hospitalized with seasonal flu in 2003-2009.

In addition, children with asthma, hemoglobinopathies such as sickle-cell disease and a history of prematurity made up a larger proportion of all children hospitalised with H1N1 influenza than with seasonal flu. However, one-third of children hospitalised with H1N1 influenza were previously healthy.

"Our findings underscore the importance of influenza immunization in children of all ages and particularly in children with underlying medical conditions," said lead author Fatimah S Dawood, epidemic intelligence service officer, Influenza Division, Centers for Disease Control and Prevention (CDC).

"Ensuring immunization of children at risk for hospitalization with influenza will remain critical during the upcoming 2010-2011 influenza season when the 2009 pandemic H1N1 virus may continue to circulate and other seasonal influenza viruses may circulate as well," Dawood added.

The 2010-2011 seasonal flu vaccine will protect against three flu viruses, one of which is a 2009 H1N1-like flu virus.

Results also showed that compared to children hospitalized with seasonal influenza, an even higher proportion of children hospitalized with H1N1 influenza were diagnosed with pneumonia and/or required intensive care.

"These findings also support the use of early antiviral treatment in children with 2009 pandemic H1N1 influenza who require hospitalisation. Prior studies of seasonal influenza have demonstrated that antiviral treatment may improve outcomes in patients with severe influenza," Dawood said.