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CERN’s CARA tool spawns valuable data on viral infection mechanisms

Accurate modelling of viral infection rates in indoor settings has been presented in detail in a peer-reviewed paper co-authored by CERN experts


CARA graphs
(Image: CERN)

CERN is renowned for being the world’s largest particle physics research laboratory and its numerous applications reach beyond this core discipline, spanning a myriad of different fields and sectors. CARA, CERN’s COVID Airborne Risk Assessment software, is a shining example of how CERN research benefits society beyond its core mission. The tool, which assesses the risk of COVID-19 infection in enclosed spaces by modelling the concentration profile of viruses with varying parameters, was recently presented in a paper published in a special issue of the Royal society’s “Interface Focus”. Along with the valuable data it revealed, it is already informing policymakers and space managers worldwide.

First developed in 2020 by CERN’s Health, Safety and Environment (HSE) expert Andre Henriques, the software was initially meant as a practical solution to the Organization’s office-sharing conundrums in the context of the pandemic. By adjusting various parameters, including mask wearing, ventilation, room volume and exposure time, space managers and safety officers could assess whether the baseline measures in place ensured an acceptable risk level and were adapted to the workplace, and this in turn helped refine CERN’s general public health measures and instructions. But the user-oriented tool soon became a wider-reaching instrument serving the fields of immunology and infectiology.

“The model we first developed was rather conservative and its accuracy, although sufficient to properly inform decision making, was hindered by the lack of relevant expertise in health science in our team. That’s when the WHO experts came in”, explains Andre Henriques. The World Health Organization (WHO) invited CERN to sit on ARIA, an international expert working group focused on developing standards for airborne transmission of respiratory pathogens. With the involvement of worldwide experts, the tool’s modelling capabilities were further optimised and refined, and the process culminated in the publication of the Interface Focus paper.

With the tool now fine-tuned thanks to expertise in health science, its models were able to successfully withstand benchmarking against both clinical data and real-life outbreaks, as presented in the paper. Among other things, CARA’s accurate modelling across various parameters was able to confirm the importance of super-emitters in airborne transmission: while these may represent only 20% of infected hosts, they are found to emit up to one hundred times more viral-containing particles. The software also provided new data corroborating the efficiency of mask wearing, as well as ventilation.

The different graphs represent the concentration profile of viruses in air over the course of a working day, including a one-hour lunch break. The relative probability of infection can be visualised by comparing the area below each graph: the larger the area, the higher the chances of being infected. (Image from the Interface Focus paper) 

With the involvement of CERN’s HSE unit, as well as the Experimental Physics (EP), Beams (BE) and Information Technology (IT) departments – not to mention the experts in the ARIA working group – the effort made and the resources mobilised to develop the technology and analyse its data were considerable. “Not only do we now have a model that is more accurate than ever, but it is also widely endorsed by the scientific community. This for me was very important because, despite the advanced expertise of the CARA team at CERN, such an endorsement from experts in health science gave the tool the necessary impetus to be recognised on a wider scale”, says Andre.

Thanks to its open-source architecture, availability and user-friendliness, the software is now being used by various organisations around the globe.