Global estimates of the direct burden of influenza on the health of younger children (under age 5 years) including separate estimates for the European RegionArchived

This Scientific Advance features a systematic review and meta-analysis of studies of burden of respiratory infections due to seasonal influenza in children published on line by the Lancet on November 11th:Global burden of respiratory infections due to seasonal influenza in young children: a systematic review and meta-analysis Nair H, Brooks WA, Katz M, et al. The Lancet, Published online November 11, 2011

It is accompanied by an editorial comment from Maria Zambon of the UK Health Protection Agency add link pleaseThis comprehensive study published by an international group attempts to estimate the global incidence of lower respiratory infections and premature deaths associated with influenza in children younger than 5 years. It is the first publication to do so and thus it is a significant contribution to expanding knowledge about the global burden of disease attributable to seasonal influenza virus in children.  The methodology was to use published and unpublished data from the author consortium to estimate the incidence of influenza episodes, influenza-associated acute lower respiratory infections (ALRI) and influenza-associated severe ALRI in children younger than 5 years, stratified by age. The data and analyses came from a systematic review of studies published between the 1st January 1995 and the 31st Oct 2010, as well as from 16 unpublished population-based studies. The authors applied these incidence estimates to global population estimates for 2008 to calculate estimates of influenza burden for that year. In addition, they estimated possible bounds for influenza-associated ALRI mortality by combining incidence estimates with case fatality ratios from hospital-based reports and identifying studies with population-based data for influenza seasonality and monthly ALRI mortality.

After applying preset criteria for inclusion the authors identified 43 suitable studies with data for around 8 million children from across the whole world. The estimates thus calculated for 2008 were that in that one year, 90 million (95% CI; 49-162 million) new cases of influenza (data from 9 studies), 20 million (13-32 million) cases of influenza-associated ALRI (13% of all cases of paediatric ALRI; data from 6 studies) and 1 million (1-2 million) cases of influenza-associated severe ALRI (7% of cases of all severe paediatric ALRI episodes; data from 39 studies) occurred worldwide in children younger than 5 years. Additionally, they estimated that approximately there were from 28’000 to 111’500 premature deaths in children younger than 5 years attributable to influenza-associated ALRI in 2008. Ninety nine percent of these deaths would have occurred in developing countries. It was noted that the incidence and mortality varied substantially from year to year in any one setting, but the authors conclude that, overall, and taking these results in consideration, influenza results in a substantial health burden worldwide.

ECDC Comment (11th November 2011):

In April this year ECDC published a Scientific Advance dealing with the burden of 2009 pandemic influenza in the general population in one European country, the Netherlands. Other studies have considered the clinical and socio-economic impact of the burden of pandemic influenza in children (1,2). What is unusual here is to have global and sub-global estimates of the burden on children from seasonal influenza.   While the burden is less in Europe than in developing countries (studies in Europe came from Finland, Germany, Spain, Switzerland and the UK) it is still significant. Scaling up from those studies suggested that the WHO European Region would experience about 1 acute lower respiratory tract infections in Europe per 1000 children per annum or a total of nearly 52,000 cases per annum in all of the WHO Region. 

Another reminder of this issue is a day of awareness-raising on November 12th – World Pneumonia Day organised by being Global Coalition against Child Pneumonia though it is appreciated that other infections and vaccine preventable diseases (Haemophilus influenza type B and Pneumococcus) also contribute to the heavy burden of pneumonia. The study shows how the pneumonia burden exists in children in Europe and part of it is due to influenza it is lower than for poorer countries. Hence it is less clear in Europe how justifiable immunising children is with flu vaccines in Europe on the basis of preventing childhood infection and pneumonia alone (there may be other reasons for immunising children as this can prevent infection in older adults). However protecting newborns is another reason for immunising pregnant women because this protects the youngest and most vulnerable children, those aged under 6 months, when they are too young for vaccine to work but their mother’s vaccine induced immunity, and maternal breast, feeding protects them.