“The most tried-and-true near-term approach, in terms of prophylaxis, is making highly potent neutralizing antibodies against the virus itself,” said George Yancopoulos, Regeneron’s co-founder and chief scientific officer, in an interview. “The landmark is to see how rapidly we could get to this point,” he said.

To battle Covid-19, Regeneron says it wants to select two antibodies against the virus, which is known as SARS-CoV-2. The antibodies target a protein on the virus’ outer shell, called the spike protein. Having two antibodies targeting the spike protein in the treatment, not one, should mean that it is more difficult for the virus to mutate in a way that will allow it to evade both antibodies.

Regeneron said in a press release that its scientists have isolated hundreds of virus-neutralizing antibodies from its mice, and more from patients who have recovered from Covid-19. It will choose two of these based on their potency and other “desirable qualities” like specificity, ability to be manufactured easily, and durability in the body.