Vaccine for tuberculosis being tested in Canada for effectiveness against COVID-19

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Canadian researchers have launched a clinical trial of an existing vaccine that may prove to be effective against COVID-19.

The vaccine, known as BCG, was originally developed to prevent tuberculosis. Administered in a single dose, the vaccine is no longer recommended for routine use in Canada where incidence of the lung disease is low. However, a raft of epidemiological studies suggests that it may be playing a broader role in reducing overall rates of respiratory disease.

“The data have shown that people who were injected [with BCG] as infants had fewer infections later on,” said Alexandre Zlotta, a urologist and surgeon with the University Health Network in Toronto, who is one of the leaders of the Canadian study.

The randomized controlled trial, which began last week, will test whether that same effect extends to COVID-19, which also attacks the respiratory tract. If it does, BCG may provide public-health officials with a safe and inexpensive vaccine option that has already been approved for use in Canada and elsewhere.

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Dr. Zlotta and colleagues are looking to recruit more than 3,600 first responders and health care workers who have an elevated risk of exposure to COVID-19. One half of the participants will be given BCG, the other half a placebo. At the end of the study, about nine months from now, researchers will compare the two groups to see if the first group has fared any better at avoiding infection by COVID-19. Preliminary results will also be examined by an independent committee at the halfway point and the trial ended early if there is strong evidence that BCG helps prevent COVID-19.

The vaccine consists of a non-reproducing version of the bacterium that causes tuberculosis and therefore cannot train the immune system to specifically recognize and target a coronavirus. Instead, researchers suspect it primes the body in a more general way and enhances its ability to seek out and destroy virus-infected cells.

Shariq Haider, an infectious-disease researcher at McMaster University in Hamilton and the trial’s other co-principal investigator, said the latest evidence in support of this premise is a study of elderly patients based in Greece, prior to the COVID-19 pandemic. The study, published last month in the journal Cell, found that those who were given the vaccine had a 70-per-cent lower rate of readmission to hospital.

“Now we have our first control data telling us there seems to be this protective effect,” Dr. Haider said.

BCG, which stands for Bacillus Calmette–Guérin vaccine, was developed early in the 20th century by Albert Calmette and Camille Guérin, two researchers at the Pasteur Institute in Lille, France. The vaccine was first tested in humans in 1921.

Since then, four billion doses of the vaccine have been administered worldwide, mostly to infants in countries with a high rate of tuberculosis. This has provided a long and detailed record of its safety, along with any adverse effects, which can include scarring at the injection site.

Sean O’Connell, a fire-prevention captain who lives in Hamilton and who volunteered for the study, said the vaccine’s extensive track record made it easy to decide to participate.

“It seemed like a good idea to get involved,” he said.

The Canadian trial is one of several around the world that is looking at the potential for BCG to reduce COVID-19 infections. Where the Canadian trial differs from many others is its use of a “recombinant" version of the vaccine, based on a bacterium that has been genetically modified to improve its ability to stoke a host’s immune system.

Jeffrey Cirillo, an infection-disease researcher at Texas A&M University who is leading a separate trial with the standard version of BCG, said he would not use a recombinant form – at least not in the United States – in order to avoid eliciting both anti-vaccination sentiments and public fear of genetically modified organisms. Neither attitudes are supported by science.

Dr. Cirillo added that BCG has received comparatively less attention from drug companies than new vaccine candidates, which are aimed directly at COVID-19, in part because there is little money to be made in producing a century-old vaccine.

“This really required academic researchers to push on it, which we’ve done,” he said.

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