Modelling virus concentration in enclosed spaces to reduce transmission
The CERN Airborne Model for Indoor Risk Assessment (CAiMIRA) is an open-source tool developed to model the concentration of viruses in enclosed spaces, to inform space-management decisions. The tool was developed at CERN in 2020 during the COVID-19 pandemic to put in place health and safety measures, such as instructions concerning the use of workspaces with the aim of minimising airborne transmission. However, work on this useful tool did not stop with the pandemic and it continues to evolve 5 years on.
The model is useful for comparing the impact and effectiveness of different mitigation measures such as ventilation, filtration, exposure time, physical activity, amount and nature of close-range interactions and the size of the room, considering both long- and short-range airborne transmission modes of airborne viruses in indoor settings.
CAiMIRA is designed to be informative, allowing the user to adapt different settings and model the relative impact on the estimated infection probabilities. The objective is to facilitate targeted decision-making and investment through comparisons, rather than a singular determination of absolute risk.
The model, described in a peer-reviewed publication, simulates the airborne spread of SARS-CoV-2 virus in a finite volume, assuming homogenous mixing for the long-range component with a two-stage jet model for short-range, and estimates the risk of COVID-19 airborne transmission therein. The report generated by the tool indicates how to avoid exceeding critical concentrations of airborne transmission in spaces such as individual offices, meeting rooms and laboratories. The model is based on scientific publications relating to airborne transmission of infectious diseases, dose-response exposures and aerosol science. The publication attracted attention and the publisher, The Royal Society, invited the corresponding author to showcase the research at the Interface seminar series.
Collaboration with the World Health Organization
CAiMIRA 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 own approach towards risk assessments for occupational hazards with the WHO’s COVID Expert Panel. As a result, WHO invited CERN to become a member of a multidisciplinary expert group of international experts. The outcome of the collaboration is a tool, ARIA, which works to define a standardised algorithm to quantify airborne transmission risk in indoor settings uses CAiMIRA at its core. This collaboration works to ensure that the model not only considers aerosol science but also virological effects, such as host-pathogen interaction.
Systematic Literature Reviews
To remain at the forefront of innovation, the CAiMIRA model must be constantly updated with the most relevant existing studies on indoor air quality. As such, a regular systematic review is considered the research methodology that provides the highest possible level of inputs into the model. However, maintaining this high level of evidence entails a huge amount of work. Thus, a new goal for CAiMIRA is to develop a mechanism to automate and support such a systematic literature review process to feed into the model, called NeutrinoReview, that is under development.
“Particle Pathways” Conference in 2025
In 2025, CAiMIRA researchers participated in the 6th Workplace and Indoor Aerosols Conference “Particle Pathways” at Gaeta, Italy, to benchmark the work. The conference, which was organised by the WHO and CERN, aimed to foster interdisciplinary collaboration, networking and innovative solutions against indoor air pollution and airborne diseases.
CERN technical contacts: Andre Henriques, Andreas Wagner, Elias Sandner, Mari Eldegard Heie, Nicola Tarocco and Nicolas Mounet.