Chest radiographs are useful for identifying cases of childhood pneumonia, but they require technical expertise and can be limited by variability between observers’ interpretations. To address these issues, in 1997 the World Health Organization (WHO) developed a standardised definitions for the interpretation of paediatric chest X-rays in epidemiological studies. These definitions were not designed for use in clinical management of individual patients. This effort was led by a Radiology Working Group of the Pneumonia Vaccine Trial Investigators’ Group, which was created to establish standardised methods for evaluating conjugate vaccines against S. pneumoniae and H. influenzae. The agreed WHO Radiological Pneumonia definition of “primary end-point pneumonia” was used as an endpoint measure in randomised clinical trials of these bacterial vaccines. By 2005, with the completion of the initial set of vaccine clinical trials with a pneumonia endpoint, WHO support for chest radiography activities declined because of staff attrition, lack of financial resources, and competing priorities. Despite this, the WHO Radiological Pneumonia definition has been used in many other epidemiological studies.

Over time, there was concern among pneumonia investigators that there had been considerable drift in the application of the standard of the WHO Radiological Pneumonia definition, alongside difficulties in access to reference materials and technical advice. These issues were reviewed at the Hib Initiative Radiology Workshop in Hanoi, Vietnam in 2011 and at the WHO PCV Impact Evaluation meeting in Geneva, Switzerland in 2013. In response to the technical needs identified at these meetings, and feedback from investigators, the WHO Chest Radiography in Epidemiological Studies (CRES) project was established to renew the activities related to the WHO standardised interpretation of paediatric chest radiographs.


The purpose of the WHO CRES project is to provide support and resources for people working on epidemiological studies that involve a radiological case definition of childhood pneumonia. This support ensures that the WHO Radiological Pneumonia definition is applied to a consistent standard and assists studies to optimise quality and safety in their radiographic methods.

What we offer

The WHO CRES project offers new resources and ongoing support for investigators, site staff, and those interpreting chest radiographs. On this website you will find:

  • Background technical and scientific materials related to the WHO standardised interpretation of paediatric chest radiographs
  • Explanation and examples of the standardised definitions, including recent clarifications
  • Access to all reference chest X-rays, plus descriptive comments and simplified illustrations where available
  • Advice on the training and standardisation of readers
  • Guidelines for assessing and optimising quality and safety in the acquisition of chest radiographs
  • Contact for technical advice and customised support for individual studies, including in-person training and centralised arbitration