WHO European Childhood Obesity Surveillance Initiative (COSI)


The WHO European Childhood Obesity Surveillance Initiative (COSI), is a unique system that for over 10 years has measured trends in overweight and obesity among primary school aged children. COSI involves taking standardized weight and height measurements from over 250 000 children across the WHO European Region, providing nationally representative data for participating countries, as well as a large Region-wide data set for analysis of the determinants of childhood overweight and obesity. This vital collaboration between WHO/Europe and research institutions from across the Region provides vital data to inform policy and practice to respond to the problem of childhood overweight and obesity.

Over 40 Member States of the Region will participate in the 5th round of COSI during the 2018–2019 school year.

About COSI

COSI was set up in response to the WHO European Ministerial Conference on Counteracting Obesity, held in Istanbul, Turkey, in 2006. Member States recognized the need for a harmonized surveillance system among primary school children to inform policy development in combating the emerging obesity epidemic in the Region. The importance of, and political commitment to, the surveillance system was reinforced in the Vienna Declaration on Nutrition and Noncommunicable Diseases in the Context of Health 2020, adopted in 2013, and the European Food and Nutrition Action Plan 2015–2020, adopted in 2014.

COSI is a survey based on nationally representative samples and takes standardized weight and height measurements. The children are measured and studied on the basis of a common protocol and approach. The first data collection took place during the 2007–2008 school year, the second round 2009–2010, the third round 2012–2013 and the fourth round 2015–2016. The fifth round is taking place during the 2018–2019 school year. COSI is now established in over 40 Member States of the Region, with the number of countries growing with each data collection round.

Since its launch in 2007, COSI has made a difference by informing policy initiatives and the public health response to the obesity epidemic in the Region. Furthermore, COSI has resulted in international and country-specific scientific publications and reports based on data collected over the past 10 years.

COSI sign-up and data collection process

All countries in the Region are encouraged to sign up for COSI.

Prior to the introduction of COSI in a Member State, the country identifies an institute with responsibility for the overall national coordination and management and assigns a principal investigator as the institute’s authorized representative. The institute then signs a collaborative agreement with WHO/Europe, defining the roles and responsibilities of the participating country and of WHO/Europe, including data release and publication policies, principles, terms and procedures.

The COSI system is simple to implement and does not consume many resources. It does not aim to replace the existing health, anthropometric and dietary surveillance systems of countries or those being planned. On the contrary, the COSI approach has the strong potential to be integrated into existing systems, where possible. The COSI protocol and manual of procedures allow each participating country to develop a system that fits its local circumstances.

WHO/Europe now offers a tool for online data collection in response to the growing number of countries participating in the initiative. This database management system, called OpenClinica, is custom prepared for interested countries, to facilitate the process. Using this platform, data can be entered directly online during data collection or afterwards from the information collected on paper.

WHO/Europe provides technical support for the implementation of COSI, and a scientific development group is advising on the continuing improvement of the survey methods and tools. WHO/Europe also offers countries training and assistance in sampling, use of equipment and the interpretation, presentation and use of data. WHO is working collaboratively with institutions across the Region to publish articles and reports using COSI data and organizes COSI network meetings every year to facilitate support and collaboration with participating countries.

Survey methods

For detailed information on the survey methods, the Childhood Obesity Surveillance Initiative (COSI) protocol outlines the common protocol agreed for use in the initiative