A vaccine that was developed a hundred years ago to fight the tuberculosis scourge in Europe is now being tested against the coronavirus by scientists eager to find a quick way to protect health care workers, among others.
The Bacillus Calmette-Guerin vaccine is still widely used in Africa, including Zambia, Zimbabwe and many other countries in the developing world, where scientists have found that it does more than prevent TB. The vaccine prevents infant deaths from a variety of causes, and sharply reduces the incidence of respiratory infections.
The vaccine seems to "train" the immune system to recognize and respond to a variety of infections, including viruses, bacteria and parasites, experts say. There is little evidence yet that the vaccine will blunt infection with the coronavirus, but a series of clinical trials may answer the question in just months.
On Monday, scientists in Melbourne, Australia, started administering the B.C.G. vaccine or a placebo to thousands of physicians, nurses, respiratory therapists and other health care workers — the first of several randomized controlled trials intended to test the vaccine's effectiveness against the coronavirus.
"Nobody is saying this is a panacea," said Nigel Curtis, an infectious diseases researcher at the University of Melbourne and Murdoch Children's Research Institute, who planned the trial. "What we want to do is reduce the time an infected health care worker is unwell, so they recover and can come back to work faster."
A clinical trial of 1,000 health care workers began 10 days ago in the Netherlands, said Dr. Mihai G. Netea, an infectious disease specialist at Radboud University Medical Center in Nijmegen. Eight hundred health care workers have already signed up. (As in Australia, half of the participants will receive a placebo.)
Dr. Denise Faustman, director of immunobiology at Massachusetts General Hospital, is seeking funding to start a clinical trial of the vaccine in health care workers in Boston as well. Preliminary results could be available in as little as four months.
"We have really strong data from clinical trials with humans — not mice — that this vaccine protects you from viral and parasitic infections," said Dr. Faustman. "I'd like to start today."
The B.C.G. vaccine has an unusual history. It was inspired in the 1800s by the observation that milkmaids did not develop tuberculosis. The vaccine is named after its inventors, Dr. Albert Calmette and Dr. Camille Guerin, who developed it in the early 1900s from mycobacterium bovis, a form of tuberculosis that infects cattle.
The scientists cultured bacterial scrapings from cow udders, and continued to culture bovine TB for over a decade until it was weak enough that it no longer caused virulent disease when given to lab animals.
The vaccine was first used in humans in 1921 and was widely adopted after World War II. Now B.C.G. is primarily used in the developing world and in countries where TB is still prevalent, where it is given to over 100 million babies a year.
Like other vaccines, B.C.G. has a specific target: TB. But evidence accumulating over the past decade suggests the vaccine also has so-called off-target effects, reducing viral illnesses, respiratory infections and sepsis, and appears to bolster the body's immune system.
The idea is an offshoot of the "hygiene hypothesis," which suggests that the modern emphasis on cleanliness has deprived children of exposure to germs. The lack of "training" has resulted in weakened immune systems, less able to resist disease.
One of the earliest studies hinting at the broad benefits of B.C.G. vaccination was a randomized trial of 2,320 babies in Guinea-Bissau in West Africa, published in 2011, that reported that death rates among low-birth-weight babies were dramatically reduced after vaccination. A follow-up trial reported that infectious-disease mortality rates in low-birth-weight babies who were vaccinated were cut by more than 40 percent.