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Why Did We Need COVID Vaccines if the TB Vaccine Offers Protection?

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Key Takeaways

  • A new study found that three doses of a vaccine for tuberculosis (TB) were 92% effective at preventing COVID-19 in patients with type 1 diabetes. 
  • It’s long been known that the TB vaccine (BCG) offers broad protection against different pathogens because of the type of immune response it prompts in the body.
  • Even though the TB vaccine could offer some protection against COVID, experts explain why we still needed COVID-specific vaccines.

In addition to being one of the most widely used vaccines in the world and having existed for 80 years, it turns out the tuberculosis vaccine might also provide protection against COVID-19.

According to a recent study published in Cell Reports Medicine, patients with type 1 diabetes who got three doses of the Bacillus Calmette-Guerin (BCG) vaccine for tuberculosis (TB) actually got some protection against COVID, too.

What is the BCG Vaccine?

The Bacillus Calmette-Guerin (BCG) vaccine provides immunity against a contagious respiratory illness called tuberculosis (TB).

Today, it’s mostly given to babies and children living in parts of the world where the disease is still common. In the United States, only specific, high-risk people get the BCG vaccine.

If a vaccine we already had can protect some people against COVID, then why did we need to make new ones? Here’s what experts say about how the BCG vaccine works and what the findings from the recent study mean for the future of vaccine development.

A Pre-COVID Study With Post-COVID Implications

While the findings ended up being COVID-relevant, the study didn’t start out being about COVID. In fact, the BCG vaccination trial was already underway before the pandemic.

The initial goal of the study was to test the effectiveness of the BCG vaccine as a treatment for long-standing type 1 diabetes (an autoimmune disease).

Before joining the study, the participants had no known exposure to TB and had not had any doses of the BCG vaccine. 

Denise Faustman, MD, PhD, a study author and the Director of Immunobiology at Massachusetts General Hospital, told Verywell that in addition to autoimmunity from the disease, people with type 1 diabetes have problems fighting infections. When the pandemic hit, the researchers were in the perfect position to study some of the most vulnerable people.

Mark Loafman, MD, MPH, a family physician and chair of the Family and Community Medicine Department at Cook County Health, was not involved in the study but can sees its value.

Loafman told Verywell that when the researchers added “a parallel arm to the study looking specifically at illness related to COVID infections” it turned out to be “a serendipitous opportunity [that] we are fortunate to be learning from.”

How Effective Was BCG Against COVID?

Several doses of the BCG vaccine were given to the patients before January 1, 2020—before there were any COVID-specific vaccines available.

There were 144 patients with type 1 diabetes in the COVID part of the study: 96 had received several doses of the BCG vaccine and 48 had only gotten a placebo.

When they followed up with the patients over about 15 months, the researchers found that about 12% of the patients who got a placebo had confirmed COVID, while just 1% of the patients who got the BCG vaccine did.

Not only did the vaccine end up being 92% effective against COVID, but the patients who got it had fewer infectious disease events and fewer symptoms (and less severe symptoms if they did get sick) than the patients who got a placebo.

Padmini Salgame, PhD, a professor in the Department of Medicine at Rutgers New Jersey Medical School, told Verywell that since the BCG vaccine appeared to offer some protection against COVID in a vulnerable, high-risk group, the results of the study could mean that the vaccine has the potential to help adults in the general population, too.

What’s Special About the BCG Vaccine?

According to Faustman, calling BCG a vaccine is a bit confusing because it’s not antigen-specific—rather, it’s the off-target effects on the immune system, including T cells, B cells, and monocytes, that make the vaccine kind of special.

The BCG vaccine contains a live version—but also a very weak version—of Mycobacterium bovis, which can cause TB in humans.

Salgame said that the BCG vaccine “induces a type of immune response referred to as ‘trained immunity’ that provides heterologous protection against a wide variety of pathogens.”

Heterologous protection means that the vaccine can encourage the body to respond to a pathogen that’s different than the one that it was exposed to from the vaccine. In a sense, trained immunity involves “reprogramming” the immune cells.

The trained immunity prompts an innate memory response in the body that provides protection against TB as well as other pathogens. Salgame said that these changes last a long time and allow the cells to respond quickly when they’re challenged by an invader.

Loafman said that most vaccines cause an antibody response to a specific virus or bacteria that cause infections. The trained immunity tactic of the BCG vaccine is one reason why it prompts a broader immune response than we see with most other vaccines.

“The epidemiological link showing a significant reduction in serious illness and death from a variety of infectious diseases among those vaccinated is remarkably strong,” said Loafman. “This added benefit has also been a reason for many countries to continue universal BCG vaccination.”

It’s not just BCG, though—other vaccines have also shown benefits beyond their effects on the targeted diseases. For example, the oral polio vaccine and measles-containing vaccines.

Why Did We Need COVID Vaccines if the BCG Vaccine Worked?

The protection from the BCG vaccine may last decades, but there’s a catch: they take a year or two to start working. So, while BCG vaccines may have offered some protection against COVID, we still needed to make vaccines that specifically targeted SARS-CoV-2—and fast.

While the main goal of vaccination is to prevent serious illness and death in people who get infected, Loafman said we shouldn’t forget about the secondary goal of vaccination: to stop the transmission of the virus even in people who don’t get really sick.

This goal was especially important during COVID because the virus experienced “variant drift” in a relatively short time. Loafman said that’s one reason why we needed COVID-specific vaccines to get the pandemic under control.

According to Salgame, the study’s findings might be more relevant to the next pandemic than the current one. Next time around, vaccines that induce trained immunity and heterologous protection could be used as the first line of defense until we can create a specific vaccine for the pathogen.

What This Means For You

Even though the vaccine that protects against TB offered some protection against COVID-19 for vulnerable patients, we still needed to make COVID-specific vaccines. However, vaccines like the one that's used for TB offer broad immunity and could be an important tool for helping us deal with the next pandemic.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. World Health Organization. BCG vaccine.

  2. Faustman DL, Lee A, Hostetter ER, et al. Multiple BCG vaccinations for prevention of COVID-19 and other infectious diseases in Type 1 diabetes. Cell Rep Med. Published online August 15, 2022. doi:10.1016/j.xcrm.2022.100728

  3. Centers for Disease Control and Prevention. Tuberculosis (TB): vaccines.

  4. Geckin B, Konstantin Föhse F, Domínguez-Andrés J, Netea MG. Trained immunity: implications for vaccination. Curr Opin Immunol. 2022;77:102190. doi:10.1016/j.coi.2022.102190

By Carla Delgado
Carla M. Delgado is a health and culture writer based in the Philippines.