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The Effect of Mask Usage on Viral Immune Escape Times: An Evolutionary Strategies-Inspired Model

The COVID-19 pandemic has posed many challenges to the world in several spaces, including the public health, economic, and political spheres. At the start of the pandemic, non-pharmaceutical interventions (NPIs) such as lockdowns, social distancing, and mask-wearing were the only tools available to combat transmission of SARS-CoV-2, the virus that causes COVID-19. More recently, several vaccines have been approved for use, and mass inoculation of the population has begun in many countries.One pressing issue is the continued use of NPIs in the context of vaccine deployment: is there an advantage to perpetuating the use of these interventions even as inoculation proceeds? The present study aims to address this question, investigating the impact of masking on the time to viral immune evasion, i.e. how masking affects the length of time the immune response is effective against the virus before the virus mutates such that it can escape the immune system. Viral immune escape is formulated as an optimization problem. A simplified and idealized model of virus transmission is proposed, and an evolutionary strategies approach is used to model the evolution of the virus.Results indicate that there is strong justification for the continued use of masks, even as vaccines are deployed. Immune escape times for no masking, 50% of the population masking, and 100% of the population masking are 17.15 ± 1.92 generations, 21.13 ± 2.33 generations, and 62.27 ± 13.68 generations respectively. This increase in viral immune escape time attributable to masking is most likely caused by decreased transmission, such that significant increases in genetic diversity are required for viral immune evasion.