Airborne Transmission of SARS-CoV-2


Currently, the existing public health measures point to the importance of proper building and environmental engineering control measures, such as proper Indoor Air Quality (IAQ). This pandemic clearly raised increased awareness on airborne transmission of respiratory viruses in indoor settings. Out of the main modes of viral transmission, the airborne route of SARS-CoV-2 seems to have a significant importance to the spread of COVID-19 infections world-wide, hence proper guidance to building engineers or facility managers, on how to prevent on-site transmission, is essential.
For information on the Airborne Transmission of SARS-CoV-2, feel free to check out the special issue on the Interface Focus journal from Royal Society publishing: Interface Focus: Volume 12, Issue 2 and an CERN HSE Seminar: https://cds.cern.ch/record/2743403.


What is CAiMIRA?


CAiMIRA stands for CERN Airborne Model for Indoor Risk Assessment, previously known as CARA - COVID Airborne Risk Assessment, developed in the spring of 2020 to better understand and quantify the risk of long-range airborne spread of SARS-CoV-2 virus in workplaces. Since then, the model has evolved and now is capable of simulating the short-range component. CAiMIRA comes with different applications that allow more or less flexibility in the input parameters: The mathematical and physical model simulate the airborne spread of SARS-CoV-2 virus in a finite volume, assuming a homogenous mixture and a two-stage exhaled jet model, and estimates the risk of COVID-19 airborne transmission therein. The results DO NOT include other known modes of SARS-CoV-2 transmission. Hence, the output from this model is only valid when the other recommended public health & safety instructions are observed, such as good hand hygiene and other barrier measures.

The methodology, mathematical equations and parameters of the model are published here in a peer-reviewed paper: Modelling airborne transmission of SARS-CoV-2 using CARA: risk assessment for enclosed spaces.

The short-range component of the model was adapted from Jia et al. (2022) Exposure and respiratory infection risk via the short-range airborne route .

The model used is based on scientific publications relating to airborne transmission of infectious diseases, virology, epidemiology and aerosol science. It can be used to compare the effectiveness of different airborne-related risk mitigation measures. The tool helps assess the potential dose of infectious airborne viruses in indoor gatherings, with people seated, standing, moving around, while breathing, speaking or shouting/singing. The model is based on the exponential dose-response of disease transmission, which assumes a fixed value for the average infectious dose. The methodology of the model is divided into five parts:
  1. Estimating the emission rate of virions;
  2. Estimating the removal rate of virions;
  3. Modeling the concentration of virions within a given volume, as a function of time;
  4. Absorbed dose of infectious viruses, inhaled during the exposure time;
  5. Estimating the probability of a COVID-19 infection (or secondary transmission) and the expected number of new cases arising from the event

What is the aim of CAiMIRA?


Although the user is able to calculate the infection probability of a stand-alone event with a pre-defined set of protection measures, the main utility of CAiMIRA is to compare the relative impact of different measures and/or combination of measure. For example:

Collaboration with the World Health Organization (WHO)


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 own approach towards risk assessments for occupational hazards, which was at the time called CARA, to WHO's COVID Expert Panel.

As a result, WHO has invited CERN to become a member of a multidisciplinary expert group of international experts called ARIA, which will work to define a standardised algorithm to quantify airborne transmission risk in indoor settings. This will ensure that the model inculdes not only the science related to aerosol science but also the virological effects, such as host-pathogen interaction.

The collaboration takes place within CERNs wide-ranging engagement with other international organisations, promoting shared solutions to societal challenges.

Main code developers:


Andre Henriques1, Luis Aleixo1, Marco Andreini1, Gabriella Azzopardi2, James Devine3, Philip Elson4, Nicolas Mounet2, Markus Kongstein Rognlien2,6, Nicola Tarocco5


1HSE Unit, Occupational Health & Safety Group, CERN
2Beams Department, Accelerators and Beam Physics Group, CERN
3Experimental Physics Department, Safety Office, CERN
4Beams Department, Controls Group, CERN
5Information Technology Department, Collaboration, Devices & Applications Group, CERN
6Norwegian University of Science and Technology (NTNU)


Other contributions from:


Anna Efimova1,2, Anel Massalimova1,3, Cole Austin Coughlin1,4, Germain Personne5

1Summer Student Programme, CERN
2M.V. Lomonosov Moscow State University
3National Research Nuclear University "MEPhI"
4University of Manitoba
5Université Clermont Auvergne


References:


Relevant literature references can be found in the paper: Modelling airborne transmission of SARS-CoV-2 using CARA: risk assessment for enclosed spaces.


Acknowledgements:


Click to expand

We wish to thank CERN at the different Departments working on the project: Occupational Health & Safety and Environmental Protection Unit, Information Technology Department, Beams Department, Experimental Physics Department, Industry, Procurement and Knowledge Transfer Department and International Relations Sector for their support to the study. We also wish to thank our collaborators at the World Health Organization (WHO) for thier endless support to this project, in particular to the members of the ARIA Expert Group.