Researchers say diseases that spread between humans and animals will become increasingly commonplace as human expansion into previously uninhabited areas intensifies.

Raj Panjabi, who leads the White House pandemic office, says that cases seen in the U.S. so far haven't been severe, and that even in larger outbreaks in poorer countries, few people have died.

Zoonotic pathogens, which include not only COVID-19 but HIV/AIDS and Ebola, have increasingly emerged because of stresses humans have placed on animal habitats, according to a United Nations report.