worth a read
the government ban applies to all experiments that might make these viruses more dangerous in any mammal.
In response to questions from NPR, an NIH spokesperson sent this explanation:
"These three agents that are subject to the pause share the characteristics of not only being human health threats " causing in some instances significant morbidity and mortality, as you know " but furthermore having the potential to be the agents of a pandemic because they are transmitted easily by respiratory droplets. So experiments that would make them even more pathogenic in mammals (and hence potentially in people) were concerning enough to warrant placing those experiments under the pause until their risks and benefits could be better characterized."
But Baric says, when it comes to SARS and MERS, there are key differences between people and mice.
"No. 1, mice don't sneeze," says Baric, so they don't transmit these diseases through the air. And he says the process of adapting these viruses to mice actually makes the germs less able to infect human cells.
"They're safer," says Baric.