Already nearly 1,500 Dutch health care workers have rolled up their sleeves for one study that Netea’s team is leading. It uses that TB vaccine, named BCG, which is made of a live but weakened bacterial cousin of the TB germ.

In Australia, researchers hope to enroll 4,000 hospital workers to test BCG, too, and 700 already have received either the TB vaccine or a dummy shot. Similar research is being planned in other countries, including the U.S.

Possibly next in line: Oral polio vaccine, drops made of live but weakened polio viruses. The Baltimore-based Global Virus Network hopes to begin similar studies with that vaccine and is in talks with health authorities, network co-founder Dr. Robert Gallo told The Associated Press.

Rapid studies are needed to tell if there could be “long-ranging effects for any second wave of this,” said Gallo, who directs the Institute of Human Virology at the University of Maryland School of Medicine.