On Jun. 10, 2020, researchers at Washington University School of Medicine in St. Louis reported they have developed a mouse model of COVID-19 that replicates the illness in people. Further, the same approach could be adopted easily by other scientists to dramatically accelerate the testing of experimental COVID-19 treatments and preventives.

The mouse model was described in a paper published online in the journal Cell. In addition to drug and vaccine testing, scientists can use the model with mice bred to develop health conditions such as obesity, diabetes or chronic lung disease to investigate why some people develop life-threatening cases of COVID-19 while others recover on their own.

Mice do not naturally get infected with the virus that causes COVID-19. To infect people, the virus latches onto a protein called angiotensin converting enzyme-2 (ACE2) on the surface of cells in the respiratory tract. But the human ACE2 protein is different from the mouse ACE2 protein, and the virus is unable to attach to the mouse version.

The virus that caused the SARS epidemic in 2003 is closely related to the one causing the COVID-19 pandemic, and the SARS virus also infects cells by latching onto the human ACE2 protein. During the SARS epidemic, researchers created a strain of genetically modified mice with the human ACE2 protein so they could study SARS. After the epidemic ended, however, interest in SARS waned and the mouse colonies were closed. The emergence of COVID-19 earlier this year triggered a frantic rush to begin breeding the mice again, but even now there are not nearly enough mice for all of the researchers who want to study the disease and to test potential vaccines and therapeutics.

The model also can be used to better understand the factors that put some people at risk of severe COVID-19 disease. Advanced age, male sex, and conditions such as obesity, diabetes, and heart, kidney or lung disease all increase risk of severe COVID-19 for reasons that are not fully understood.