While no laboratory method or model is infallible, it has proven to be exceedingly difficult to create an accurate animal model for COVID-19 that replicates a severe human infection. Reasons include:

• model organisms typically do not have the risk factors for COVID-19 that humans do (ex: old age, diabetes, cardiovascular disease)
• animals, including hamsters, ferrets, and nonhuman primates, seem to only develop mild symptoms and recover when infected with SARS-CoV-2
• conventional mouse models are ineffective because mouse ACE2 does not efficiently bind with SARS-CoV-2 S protein