Prior to World Pneumonia Day (Sat 12 Nov) a study published Online First in The Lancet for the first time provides global estimates of seasonal influenza in children below the age of five years and the resultant burden of influenza-related pneumonia. According to the study, the researchers estimate that globally approximately 90 million children contract seasonal flu each year, resulting in around 1 million hospital admissions and almost 111,500 deaths due to influenza-related pneumonia, with 99% of these deaths occurring in developing countries.
Because researchers cannot 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), 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In developing countries, a large amount of incidence and mortality data from influenza-linked pneumonia remains unpublished. The authors, Dr Harish Nair from the Centre for Population Health Sciences at the Medical School at The University of Edinburgh, UK, and his global team therefore decided to form an international Influenza Study Group, to supplement their systematic literature review, which contains published data from high-income and developing countries with available unpublished data.
By identifying 43 suitable studies containing data for around 8 million children, they estimated that worldwide about 90 million new cases of influenza occurred in children below the age of 5 years, together with 20 million cases of pneumonia caused by influenza. This represents approximately 13% or 1 in 8 cases of all pediatric pneumonia globally.
The researchers estimated about 1 million cases of influenza-linked severe pneumonia, representing 7% or 1 in 14 of all severe pediatric pneumonia cases globally. Other estimates indicate that between 28,000 and 111,500 children below the age of 5 years died in 2008 due to influenza-linked pneumonia with 99% of deaths occurring in developing countries.
The researchers discovered that from year to year incidence and mortality rates varied significantly in any one setting. Data to provide global incidence estimates by influenza type or subtype was insufficient, although it was observed that the incidence rate of Influenza A was generally higher than that of Influenza B.
In a concluding statement the authors say:
“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. Our report should also help inform donor agencies in assigning funding priorities for novel vaccine development and implementation or other influenza prevention strategies. Until the widespread implementation of an effective influenza vaccine is achievable, reliable provision of effective case management (including oxygen therapy for hypoxemia and antibiotic treatment of secondary bacterial infections) will substantially reduce sequelae and mortality associated with this disease.”
Dr Maria Zambon from the Health Protection Agency in London, UK, says in a linked comment:
“Importantly, Nair and colleagues’ study concludes that most childhood mortality occurs outside of hospital settings, with roughly 15-fold differences of case fatality ratio between developing and developed countries. Most of the world’s children live in the developing world. This finding is confirmation of the high disease burden caused by influenza in the youngest age groups, even if the exact numbers are obscure.”
She adds the need to set priorities for health interventions with local evidence to inform decision makers, concluding:
“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.”
Written by Petra Rattue