AFP reports on a study conducted in Hong Kong that suggests that wearing face masks substantially reduces transmission of Covid-19... between hamsters.
The Hong Kong researchers placed face masks between two cages of hamsters, after infecting the inhabitants of one cage with coronavirus; another two cages provided the control study, without face masks.
Around 65% of the healthy hamsters freely exposed to air circulating from the infected animals contracted Covid-19, as opposed to just 15% of the protected hamsters. This applied when the masks were placed on the cage containing the infected animals; when the masks were placed on the cage holding the healthy animals, the transmission rate rose to 35%.