CERN working with WHO to improve understanding of COVID-19 airborne transmission risk in indoor spaces


CARA illustration
CARA illustration (Image: CERN)

Editor update 13/3/23: Please note that since September 2022 CARA is now called CAiMIRA - CERN Airborne Model for Indoor Risk Assessment.


As the response to the pandemic evolves and people step back into the office, it is necessary to monitor continuously the risk of disease transmission and be prepared to make quick, evidence-based decisions to ensure that everyone can work safely.

CERN has developed the COVID Airborne Risk Assessment tool (CARA) to help personnel return to work safely by assessing the risk of COVID-19 infection in enclosed spaces like offices or meeting rooms. In accordance with CERN’s knowledge-transfer strategy, CERN has made the CARA software open-source, and the tool is freely available to all on GitLab

The tool has attracted the attention of many international organisations, including the World Health Organization (WHO) and the United Nations Office at Geneva (UNOG). In June 2021, CERN shared its approach to risk assessment of occupational hazards, presenting CARA to WHO’s COVID Expert Panel. As a result, WHO has now invited CERN to become a member of a multidisciplinary working group of international experts, which will work to define a standardised algorithm to quantify airborne transmission risk in indoor settings. The collaboration takes place within CERN’s wide-ranging engagement with other international organisations, promoting shared solutions to societal challenges.

Since the beginning of the COVID-19 pandemic, WHO has worked closely with a wide range of experts from diverse technical disciplines and organisations on gathering evidence, developing and updating guidance, including on the research on modes of transmission of SARS-CoV-2, and related infection prevention and control recommendations. The CARA tool developed by CERN is an innovative approach to estimating the risk and informing space-management decisions for a safe return to work,

says Maria Van Kerkhove, WHO COVID-19 Technical Lead.

With the expertise and competence of medical and health professionals from the WHO worldwide community, it could eventually be possible to harness CERN’s CARA tool for wider applications that benefit society,

says Archana Sharma, Senior Adviser for Relations with International Organisations, who coordinates CERN’s relations with WHO.

The CARA tool models the concentration profile of potential airborne viruses when people breathe or speak in enclosed spaces, producing clear and intuitive graphs. The user can set a number of parameters, including room volume, exposure time, activity type, mask-wearing and ventilation. The report generated by the tool indicates how to avoid exceeding critical concentrations and break chains of airborne transmission in spaces such as individual offices, meeting rooms and labs. The tool can scientifically assess the risk for different factors like: Is there a need for filtration systems in the room? What if a speaker at a meeting removes their mask? This information is then used by space managers and safety officers to implement the necessary safety measures and invest in targeted technical solutions.

Even with the vaccination campaigns in full swing in many countries, we are still seeing high numbers of positive cases and we must not forget that the virus is still out there. CARA is an easy-to-use tool that can be pivotal in helping people return safely to social spaces,

says Benoît Delille, Head of the Occupational Health, Safety and Environmental Protection (HSE) unit at CERN.

The software is constantly being improved with the help of experts at CERN and across the world.

CARA has a lot of potential and we are exploring its biomedical applications with other collaborators like the Institute of Global Health at the University of Geneva,

says Alessandro Raimondo from the CERN Knowledge Transfer group.

Learning from such synergetic experiences, CERN’s hope is to make the tool’s use and integration simpler and smoother in various places worldwide as part of the collective effort to take a firm stand against the pandemic.


CERN’s technologies and expertise are available for scientific and commercial purposes through a variety of technology transfer opportunities. The CERN Knowledge Transfer group can help you tap into this potential and find solutions for you based on CERN’s many areas of expertise. Visit the KT website or write to us at