DAVID GREENE, HOST:
Scientists are working at a record-breaking pace to develop a COVID-19 vaccine, but it likely won't be available for many Americans until at least next summer. In the meantime, scientists are looking for something that's already in their toolbox that could slow the spread of the disease quickly. Some researchers are excited about a vaccine for an entirely different disease, one developed more than a century ago. Here's NPR's Michaeleen Doucleff.
MICHAELEEN DOUCLEFF, BYLINE: In the early 1900s, two French scientists took on one of the most deadly diseases, tuberculosis. At the time, TB was killing three times as many people per capita as COVID is today. And there was no vaccine. So these French guys decided to try to develop one for TB. They used what was the most effective approach at the time, live bacteria. Dr. Daniel Hoft is a TB expert at Saint Louis University. He says the scientists took a strain of TB from cows and grew it in the lab for a long time.
DANIEL HOFT: Left it unattended for about nine years, but it continued to slowly grow.
DOUCLEFF: And weaken. The scientists waited until the TB bacteria were just weak enough not to make people sick but still strong enough to trigger an immune response.
HOFT: They decided to use it.
DOUCLEFF: And they found it didn't make people sick. In fact, it protected babies against TB, cutting their risk of a deadly infection by up to 70%. It was a game-changer.
HOFT: It caught off like wildfire and has been, if not the most commonly used vaccine in the world ever since...
DOUCLEFF: The vaccine is called BCG. And over the past century, scientists have noticed something surprising. It not only protects babies against TB, but it also protects them against many deadly childhood infections.
BARDIA AMIRLAK: In the 1920s in Sweden, the kids who got BCG at birth - they had threefold decrease in mortality.
DOUCLEFF: That's Dr. Bardia Amirlak at the UT Southwestern Medical Center. He says scientists don't understand exactly how BCG fights off other diseases, but there's evidence that it's not just BCG that can do this but any live vaccine, such as polio, measles and even the live flu vaccine. Robert Gallo directs the Institute of Human Virology at the University of Maryland School of Medicine. He was one of the main scientists involved in the discovery of HIV. He says live vaccines supercharge the body's frontline defenders, the cells that first notice an invader and attack it.
ROBERT GALLO: And they yell out a scream - help. It triggers off a lot of mechanisms to stop this infection immediately.
DOUCLEFF: Now Gallo and scientists are wondering if BCG or another live vaccine can help a person clear out COVID-19 more quickly so they not only don't get sick, they aren't contagious.
GALLO: And if enough people were protected for a period of time, you wouldn't be spreading the virus. We could break the back of the epidemic.
DOUCLEFF: To test this hypothesis, scientists around the world are running more than a dozen clinical trials with BCG. Dr. Moshe Arditi leads one of them at Cedars-Sinai in Los Angeles. He says we already know BCG is safe.
MOSHE ARDITI: More than 130 million kids every year - every year - receive the BCG vaccine. So the safety profile has been very strong.
DOUCLEFF: And it's cheap - just a few dollars per dose. The big question is, how effective will it be? Arditi says no one believes BCG will be better than a specific vaccine for COVID-19, but it could be approved and available more quickly, even by early next year.
ARDITI: This is just to have a bridge until we have the most effective, the most safe vaccine.
DOUCLEFF: And how ironic would it be if the key to stopping the world's newest disease is one of our oldest vaccines?
Michaeleen Doucleff, NPR News. Transcript provided by NPR, Copyright NPR.