SARS-CoV-2 transmission: The cigarette smoke analogy

Despite the current presumption that SARS-CoV-2 is transmitted by droplets, the reported evidence of the presence of the virus in air suggests that droplets dry fast producing clusters of virus, which are most penetrative through commonly available fabric filters to the public. We consider droplets corresponding to a typical bimodal distribution of droplets of sneeze and calculate the time taken for them to evaporate to their ultimate size for two virus loadings. The dry virus clusters resulting from fine droplets of the first mode have a size distribution comparable to cigarette smoke. There are currently no masks available to the public which can filter these aerosols efficiently, and even FFP grade masks have low filtration efficiency for these particle sizes. The implications are that safe distance is considerably greater than the generally-recommended two metres, as the virus remains fully suspended in the air. Secondly, mask filters available to the public are inefficient in preventing SARS-CoV-2 spreading, as it could penetrate through them. The rapid spread of the virus is indicative of the ease with which it spreads through the air, and apart from wearing a high efficiency mask, the only safe prevention is to self-isolate at home.