Scientists are dusting off some decades-old vaccines against other germs to see if they could provide a little stopgap protection against COVID-19 until a more precise shot arrives.
It may sound odd: Vaccines are designed to target a specific disease. But vaccines made using live strains of bacteria or viruses seem to boost the immune system's first line of defense, a more general way to guard against germs. And history books show that sometimes translates into at least some cross-protection against other, completely different bugs.
There's no evidence yet that the approach would rev up the immune system enough to matter against the new coronavirus. But given that a brand-new vaccine is expected to take 12 to 18 months, some researchers say it's time to put this approach to a faster test, starting with a tuberculosis vaccine.
"This is still a hypothesis," said Dr. Mihai Netea of Radboud University Medical Center in the Netherlands. But if it works, "it could be a very important tool to bridge this dangerous period until we have on the market a proper, specific vaccine."
The World Health Organization issued a stern warning Monday not to use the TB vaccine against COVD-19, unless and until studies prove it works.
Already nearly 1,500 Dutch healthcare 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.
At the U.S. National Institutes of Health, researchers are in early discussions about proposals to study the TB and polio vaccines as a possible COVID-19 defense, said agency spokeswoman Jennifer Routh.
There's a big caution: Live vaccines are risky for people with weakened immune systems, and shouldn't be tried against COVID-19 outside of a research trial, said Dr. Denise Faustman, immunobiology chief at Massachusetts General Hospital, who is planning a TB vaccine study.
"You can't just roll it out," she stressed. But, "it's kind of an amazing opportunity to prove or disprove this off-target effect."