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Pneumonia kills 900,000, infects 100m kids yearly


Results from seven-country project indicate that pneumonia kills 900,000 children under five years old and more than 100 million cases reported each year worldwide.

Results from seven-country project indicate that pneumonia kills 900,000 children under five years old and more than 100 million cases reported each year worldwide.

According to the study from a consortium of scientists from around the world, led by a team at the Johns Hopkins Bloomberg School of Public Health, United States, this makes pneumonia a greater cause of childhood mortality than malaria, tuberculosis (TB), Human Immuno-deficiency Virus (HIV), Zika virus and Ebola virus combined.

The study embargoed to be published today in The Lancet journal highlights need for new vaccines, especially against respiratory syncytial virus.


Respiratory syncytial virus (RSV) and other viruses now appear to be the main causes of severe childhood pneumonia in low- and middle-income countries, highlighting the need for vaccines against these pathogens.

The study is titled “Causes of severe pneumonia requiring hospital admission in children without HIV infection from Africa and Asia: the PERCH multi-country case-control study.”

The study was carried out at sites in Bangladesh, The Gambia, Kenya, Mali, South Africa, Thailand, and Zambia.

The study was the largest and most comprehensive of its kind since the 1980s. It included nearly 10,000 children in seven African and Asian countries. After testing for viruses, bacteria, and other pathogens in children with severe hospitalized pneumonia—and in community children without pneumonia—the study found that 61 percent of severe pneumonia cases were caused by viruses led by RSV, which alone accounted for 31 percent of cases.

Study co-principal investigator Maria Deloria Knoll, PhD, a senior scientist in the Bloomberg School’s Department of International Health, and associate director of science at the Johns Hopkins International Vaccine Access Center (IVAC), said: “Prior to this study, we didn’t know which specific viruses and bacteria are now causing most of the severe childhood pneumonia cases in the world, but public health organizations and vaccine manufacturers really need that information to work toward reducing the substantial childhood mortality that pneumonia still causes.”


According to the researchers, identifying the germs that cause pneumonia is difficult in individual cases and much more so on a scale of thousands of cases, especially in low- and middle-income countries where most pneumonia deaths occur.

Researchers in prior pneumonia studies simply lacked the microbiological and analytical resources to produce estimates of the major pneumonia pathogens, Knoll says. And, in the past two decades, many low- and middle-income countries have introduced effective vaccines against known major bacterial causes of pneumonia—Haemophilus influenzae type b and Streptococcus pneumoniae—so the global mix of pathogens causing childhood pneumonia has changed as a result.

The new, IVAC-led study, known as the Pneumonia Etiology Research for Child Health (PERCH) study, included 4,232 cases of severe hospitalized pneumonia among children under five years and 5,325 community children without pneumonia during a two-year period.

PERCH was supported by grant 48968 from The Bill & Melinda Gates Foundation.

For their study, researchers took nasal and throat swabs as well as blood, sputum and other fluid samples from cases and controls and tested them for pathogens using state-of-the-art laboratory techniques. Cases for the primary analysis were limited to those whose pneumonia was confirmed by chest X-ray, and children with HIV were considered in a separate analysis because the causes of their pneumonia would likely differ from those without HIV.


With analytic methods unique for an etiology study, the researchers compared the pathogens found in samples from severe pneumonia cases to those from other children in the community in order to estimate the likeliest cause of each case. In this way they were able to identify the leading causes of childhood pneumonia among children in these settings.

The researchers concluded that, across all study sites combined, viruses accounted for 61.4 percent of cases, bacteria for 27.3 percent of cases, Mycobacterium tuberculosis for 5.9 percent of cases. Fungal and unknown causes accounted for the remainder of cases.

RSV accounted for nearly a third of all cases and was the leading cause of severe pneumonia in each of the seven countries studied. Other top causes were rhinovirus, human metapneumovirus, parainfluenza viruses, and S. pneumoniae bacteria.

A professor at the Johns Hopkins Bloomberg School of Public Health and now serves as Director of Immunizations, Vaccines and Biologicals at the World Health Organization, who led the PERCH study, Dr. Katherine O’Brien, said: “We now have a much better idea of which new vaccines would have the most impact in terms of reducing illness and mortality from childhood pneumonia in these countries.”

RSV has long been known as a common and potentially serious respiratory pathogen among children and the elderly. It remains the leading cause of pneumonia in children younger than one year in the United States, according to the Center for Disease Control and Prevention. Several RSV vaccine candidates are being developed and evaluated in clinical trials. A monoclonal antibody therapy, palivizumab, is available for the prevention of RSV disease in children with underlying medical conditions but is not suitable programmatically or financially for widespread use in routine immunization programmes.

The analytical technique developed for the study to estimate the cause of individual cases of childhood pneumonia is called the Bayesian Analysis Kit for Etiology Research (BAKER), and is available online as an open-source application for use by other public health researchers.

Malone Professor of Biostatistics in the Bloomberg School’s Department of Biostatistics, Dr. Scott Zeger, said: “Estimating the etiology of pneumonia was like a complex jigsaw puzzle where the picture could only be seen clearly by assembling multiple, different pieces of information using innovative epidemiologic and statistical methods.”

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