Fig. 2.

Fomite-mediated SARS-CoV-2 infection risks associated with individual and combined standard infection control interventions (hourly handwashing of ungloved hands [2 log₁₀ virus removal efficiency] (Grove et al., 2015), surgical masking). Vaccination was incorporated into the model representing two doses of mRNA vaccine (Moderna/Pfizer) and was applied with and without the standard infection control interventions. Additional decontamination of plastic packaging [3 log₁₀ virus removal efficiency] (EPA, 2020) was applied in combination with the standard infection control interventions. Ventilation (two air changes per hour [ACH]) was applied to all simulations. An infectious to non-infectious particle ratio of 1:100 (Pitol & Julian, 2021) was applied to all viral shedding concentrations. Reductions in SARS-CoV-2 infection risk (%) to the susceptible worker relative to no interventions are reported below each panel. Panel A represents the impact of standard infection control interventions with and without vaccination on fomite-mediated SARS-CoV-2 risk. For the first vaccination scenario, we assumed only the susceptible worker was vaccinated with two doses of mRNA vaccine (Moderna/Pfizer) and vaccine effectiveness (VE) against susceptibility to infection was simulated across three vaccination states. These included: 1) no vaccination/no prior immunity; 2) lower VE ranging from 64% (Moustsen-Helms et al., 2021) - 80% (Khan & Mahmud, 2021) representative of reduced protection (variants of concern, waning immunity, immunocompromised and elderly or at-risk populations); and 3) optimal VE ranging from 86% (Andrejko et al., 2021; Pawlowski et al., 2021) – 99% (Swift et al., 2021) among healthy adults 14 days or more after second mRNA dose. Panel B: the second vaccine scenario represented vaccine effectiveness against transmission, where all workers are assumed to be vaccinated with two doses of mRNA vaccines and hence the model simulated breakthrough infections. Vaccine effectiveness against transmission (VET) was modeled by applying the combined effect of the reduction in risk of infection to the susceptible worker and the risk of transmissibility given a breakthrough infection among the vaccinated workers. We used the VET estimate (88.5% [95% CI: 82.3%, 94.8%]) derived from Prunas et al. (2021). VET was modeled across a range of three peak infectious viral shedding concentrations representative of possible increased transmissibility and/or infectiousness of variants of concern: 1) 8.1–9.4 log₁₀ viral particles; 2) 7.1–8.4 log₁₀ viral particles; and 3) 6.4–7.7 log₁₀ viral particles. These viral shedding levels represent 100-, 10-, and 2-times, respectively, the increased viral shedding concentration simulated in the base model analysis. Dashed lines represent 1:10,000 (black) and 1:1,000,000 (gray) infection risk targets. Results are presented as the median risk values with 5th and 95th percentile bars.