Approximately 90 million children contract seasonal flu each year, resulting in around 1 million hospitalizations and nearly 111,500 deaths due to influenza-related pneumonia, most of which occur in developing countries, according to a study
published in The Lancet
The study is the first of its kind to provide global estimates of seasonal influenza in children under the age of 5 and the resultant burden of influenza-related pneumonia.
Previously, researchers have not been able to fully explain the pediatric pneumonia burden based on recent estimates of global pneumonia incidence and mortality linked to Streptococcus pneumoniae, Haemophilus influenza type b, and respiratory syncytial virus (RSV). Therefore, they needed to investigate the role of other pathogens, such as the influenza virus, which is linked to a large but unknown number of hospital admissions in young children globally and can be prevented through vaccination.
In developing countries, a large amount of incidence and mortality data from influenza-linked pneumonia remains unpublished, which led Harish Nair, MD, of the University of Edinburgh, and colleagues to form an international Influenza Study Group, to supplement their systematic literature review, which includes studies published between 1995 and 2010, along with unpublished population-based studies.
Analysis of 43 studies containing data for around 8 million children determined that about 90 million new flu cases occurred in children under the age of 5 years, along with 20 million cases of pneumonia caused by influenza. This represents approximately 13% of all pediatric pneumonia globally.
Dr. Nair and colleagues estimated about 1 million cases of influenza-linked severe pneumonia, representing 7% of all severe pediatric pneumonia cases globally. Other estimates indicated that between 28,000 and 111,500 children younger than age 5 died in 2008 due to influenza-linked pneumonia, with 99% of deaths occurring in developing countries.
From year to year, incidence and mortality rates were found to vary significantly in any one setting, they found. Data to provide global incidence estimates by influenza type or subtype was insufficient; however, it was observed that the incidence rate of Influenza A was generally higher than that of Influenza B.
“Influenza is the second most common pathogen identified in children with acute lower respiratory infection [pneumonia] and contributes substantially to the burden of hospitalization and mortality in young children. Our estimates should inform public health policy and vaccine strategy, especially in developing countries,” the authors wrote.
In a related commentary
also published in The Lancet
, Maria Zambon, PhD, of the Health Protection Agency in London, said the study confirms that “most childhood mortality occurs outside of the hospital settings,” and highlights the differences in fatality ratio between developing and developed countries. Noting that most children live in developing countries, she added, “This finding is confirmation of the high disease burden caused by influenza in the youngest age groups, even if the exact numbers are obscure.”
Dr. Zambon also emphasized the need to establish priorities for health interventions with local evidence to inform decision makers. “Robust, evidence-based comparisons of health interventions, such as selective versus universal vaccination policies between different countries and regions, are essential to help decision makers with restricted resources who are trying to get the best return for the lowest cost,” she added.