1. "Prophylactic or therapeutic administration of neomycin provided significant protection against upper respiratory infection and lethal disease in a mouse model of COVID-19." 2. "Furthermore, neomycin treatment protected Mx1 congenic mice from upper and lower respiratory infections with a highly virulent strain of influenza A virus. " 3. "In Syrian hamsters, neomycin treatment potently mitigated contact transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)." 4. "In healthy humans, intranasal application of neomycin-containing Neosporin ointment was well tolerated and effective at inducing ISG expression in the nose in a subset of participants."

The mechanism appears to be that Neosporin triggers an ISG[1] (immune) response? Not a biologist etc, but the results showing that it prevents transmission is only in rodent models, and then showing that a similar biomarker shows up in (some of) the participants and the rodent models. They authors say:

> "These findings suggest that neomycin has the potential to be harnessed as a host-directed antiviral strategy for the prevention and treatment of respiratory viral infections."

[1]