  To optimize strategies for curbing the transmission of airborne pathogens,
the efficacy of three key controls -- face masks, ventilation, and physical
distancing -- must be well understood. In this study we used the
Quadrature-based model of Respiratory Aerosol and Droplets to quantify the
reduction in exposure to airborne pathogens from various combinations of
controls. For each combination of controls, we simulated thousands of scenarios
that represent the tremendous variability in factors governing airborne
transmission and the efficacy of mitigation strategies. While the efficacy of
any individual control was highly variable among scenarios, combining universal
mask-wearing with distancing of 1~m or more reduced the median exposure by more
than 99\% relative to a close, unmasked conversation, with further reductions
if ventilation is also enhanced. The large reductions in exposure to airborne
pathogens translated to large reductions in the risk of initial infection in a
new host. These findings suggest that layering controls is highly effective for
reducing transmission of airborne pathogens and will be critical for curbing
outbreaks of novel viruses in the future.
