Mean time to infection by small diffusing droplets containing SARS-CoV-2 during close social contacts

Dobramysl, U.; Sieben, C.; holcman, D.

Airborne viruses such as SARS-CoV-2 are partly spreading through aerosols containing viral particles. Inhalation of infectious airborne particles can lead to infection, a route that can even be more predominant compared with droplet or contact transmission. To study the transmission between a susceptible and an infected person, we estimate the distribution of arrival times of small diffusing aerosol particles to the inhaled region located below the nose until the number of particles reaches a critical threshold. Our results suggest that although contamination by continuous respiration can take around 90 minutes at a distance of one meter, it is reduced to a few minutes when coughing or sneezing. Interestingly, there is not much differences between outdoors and indoors when the air is still. When a window is open inside an office, the infection time is reduced. Finally, wearing a mask leads to a delay in the time to infection. To conclude, diffusion analysis provides several key time scale of viral airborne transmission.