CDC Collaborative Study: Influenza Important Cause of Respiratory Hospitalizations Worldwide

A study by CDC authors and global partners published today in the journal PLOS Medicine looked at influenza surveillance data from 350 sites in 60 countries and found that influenza was responsible for about 10% of respiratory hospitalizations in all children younger than 18 years worldwide, with a range by age group of 5% to 16%. The highest proportion of respiratory hospitalizations attributed to flu occurred among children 5 years to 17 years of age. The study is the first to look at global flu-associated hospitalizations in that age group. The study also broke down hospitalizations by region and found that the majority of flu-associated hospitalizations in young children occur in developing countries. Study authors suggest that increasing influenza vaccination coverage among young children and pregnant women worldwide could reduce this burden.

Over the past decade, systematic surveillance and testing for influenza among hospitalized children has expanded globally. Experts were able to use these surveillance data to produce global estimates of influenza disease burden in children. As part of this effort, CDC established the Global Respiratory Hospitalizations – Influenza Proportion Positive (GRIPP) working group, with collaborators from 60 countries. The study looked at data collected from GRIPP working group members and a systematic literature review, which resulted in a database of flu-associated hospitalization data worldwide spanning a 31-year period from 1982 to 2012. The study estimates the proportion of respiratory hospitalizations caused by influenza infection among children younger than 6 months (5%), children younger than 1 year (6%), children younger than 2 years (7%), children younger than 5 years (7%), children 5 years to 17 years (16%), and all children younger than 18 years (10%).

The study translates the above proportions into numerical estimates of 870,000 influenza-associated respiratory hospitalizations in children younger than 5 years, 374,000 in children younger than 1 year, and 228,000 in children younger than 6 months. An earlier study published in 2013, estimated that 911,000 flu-associated hospitalizations occur yearly among children younger than five. The new study, which used data from more countries and a different methodology, corroborates this earlier finding. The study also reported that more than half of the estimated 870,000 flu hospitalizations associated with respiratory illness in children younger than 5 years occur in Africa (253,000) and Southeast Asia (278,000).

These estimates expand knowledge of the impact of severe influenza among children, particularly children in the developing world, and support the evidence base for vaccination of children and pregnant women worldwide. Vaccination of pregnant women has been found to offer protective benefit for the infant for several months after birth. Countries considering possible influenza vaccination programs for children and/or pregnant women can use these numbers to estimate the impact of vaccination on number of cases averted or costs saved.

Ongoing efforts in the working group include a similar analysis for influenza-associated hospitalizations among adults and determining a denominator of global respiratory hospitalizations among those older than 5 years of age.

For more information about children and flu, visit Children, the Flu, and the Flu Vaccine

The study is available online in PLOS Medicine.