In an October NEJM article it was stated that:
Recent virologic, epidemiologic, and ecologic data have led to the hypothesis that facial masking may also reduce the severity of disease among people who do become infected. This possibility is consistent with a long-standing theory of viral pathogenesis, which holds that the severity of disease is proportionate to the viral inoculum received. Since 1938, researchers have explored, primarily in animal models, the concept of the lethal dose of a virus — or the dose at which 50% of exposed hosts die (LD50). With viral infections in which host immune responses play a predominant role in viral pathogenesis, such as SARS-CoV-2, high doses of viral inoculum can overwhelm and dysregulate innate immune defenses, increasing the severity of disease. Indeed, down-regulating immunopathology is one mechanism by which dexamethasone improves outcomes in severe Covid-19 infection. As proof of concept of viral inocula influencing disease manifestations, higher doses of administered virus led to more severe manifestations of Covid-19 in a Syrian hamster model of SARS-CoV-2 infection.
citing: Imai M, Iwatsuki-Horimoto K, Hatta M, et al. Syrian hamsters as a small animal model for SARS-CoV-2 infection and countermeasure development. Proc Natl Acad Sci U S A 2020;117:16587-16595.
Have there been any replications of this finding? (If they exist they are almost certainly in other animal models, which there are a few for Covid-19.)
I see mentioned on CNN that there might be a similar study in ferrets, but I can't locate it:
"I don't think we're going to actually get to that value. We can in animals -- there's been a ferret model and there's been a hamster model -- now two animal models where the more you give them the more sick those animals get and that is helpful, and it may give us a sense. But we won't know with humans, unfortunately, how much it takes," she [Dr. Monica Gandhi, an infectious disease doctor and professor of medicine at the University of California, San Francisco] said.
(Interestingly enough, it seems no animal model managed to reproduce severe Covid-19 as seen in humans, i.e. ARDS and coagulopathy outcomes.)