When a rare but deadly rodent-borne virus struck passengers on a cruise ship and seemed to be spreading, there were no treatments for those who fell ill and no vaccines to protect others.

That was the case even though it wasn’t a novel germ that the world had never seen before, like the virus that caused the coronavirus pandemic. It was a hantavirus, one of a family of viruses that have been known for decades and are thought to exist around the world.

Teams of researchers, including those in Chile, Argentina and the United States, have long been trying to find and develop drugs and vaccines. But because the viruses are relatively rare and do not spread easily between people, there has not been enough sustained investment by governments, global health groups or drug companies to pay for the extensive safety and efficacy testing needed to make them available.