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Century-old vaccine protects diabetics from severe COVID-19 and other infectious diseases

Century-old Bacillus Calmette-Guérin (BCG) vaccine, originally developed to combat tuberculosis, offers significant protection to individuals with type 1 diabetes.
Century-old Bacillus Calmette-Guérin (BCG) vaccine, originally developed to combat tuberculosis, offers significant protection to individuals with type 1 diabetes. (CREDIT: Creative Commons)

In a groundbreaking study, researchers at Massachusetts General Hospital (MGH) have discovered that the century-old Bacillus Calmette-Guérin (BCG) vaccine, originally developed to combat tuberculosis, offers significant protection to individuals with type 1 diabetes against severe COVID-19 and other infectious diseases.

Two rigorous, randomized, double-blind, placebo-controlled trials revealed that the BCG vaccine provided consistent protection throughout nearly the entire COVID-19 pandemic in the United States, regardless of the viral variant involved.


“Individuals with type 1 diabetes are highly susceptible to infectious diseases and had worse outcomes when they were infected with the SARS-CoV-2 virus,” said Dr. Denise Faustman, senior author and director of the Immunobiology Laboratory at MGH, and an Associate Professor of Medicine at Harvard Medical School. “Published data from other investigators show mRNA COVID-19 vaccines are not very effective in this group of vulnerable patients. But we’ve shown that BCG can protect type 1 diabetics from COVID-19 and other infectious diseases.”

BCG vaccination study graphical abstract.
BCG vaccination study graphical abstract. (CREDIT: Cell Reports Medicine)

The Phase III trial, lasting 18 months and published in iScience, was conducted late in the US pandemic when the Omicron variant was prevalent. An earlier 15-month Phase II trial took place early in the pandemic, with results published in Cell Reports Medicine.


During the pandemic, numerous international trials examined if a single shot or booster of BCG, given to previously vaccinated adults, could protect them from infection and COVID-19.

This research added to a substantial global clinical trial database indicating that BCG given to newborns may protect against various infectious diseases for decades. However, the results of these booster trials were mixed, with five randomized trials showing efficacy and seven showing no benefit.


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The MGH trials stood out due to several key differences. Instead of a single dose, participants received five or six doses of a particularly potent BCG strain. Additionally, US participants were monitored for 36 months, significantly longer than in other studies.

“We know that in people who are naïve to BCG vaccine, the off-target effects can take at least two years to achieve full protection,” Faustman explained. “Giving multiple doses of the vaccine may speed up that process.”


Moreover, the US population had never received BCG vaccines before, meaning these trials were not booster trials. “The Phase II and Phase III trials conducted at MGH were unique in that they were the only COVID trials in the world where the study population had never received a BCG vaccine and had never been exposed to TB,” Faustman noted. “Trials in countries where participants had received BCG as newborns or had previous exposure to tuberculosis may have obscured any benefit from a BCG booster.”

The MGH trials included 141 participants with type 1 diabetes. Among them, 93 individuals in the treatment group received five or six doses of BCG, while 48 in the placebo group received a sham vaccine. Participants were followed for 36 months to account for diverse COVID-19 genetic variants and various infectious disease exposures.

In the Phase II trial (January 2020 to April 2021), conducted when the virus was more lethal but less transmissible, the BCG vaccine’s efficacy was 92%, comparable to the efficacy of the Pfizer and Moderna vaccines in healthy adults.


Over the full 34 months of the US COVID-19 pandemic, the BCG vaccine demonstrated a significant efficacy of 54.3%. Researchers also found that BCG-treated participants had lower rates of viral, bacterial, and fungal infections, as well as reduced incidence of COVID-19 itself.

The BCG vaccine provides immunity likely lasting decades, offering a clear advantage over COVID-19 vaccines and vaccines for other infectious diseases, such as influenza, where effectiveness only lasts two or three months. “The BCG vaccine offers the prospect of near-lifelong protection against every variant of COVID-19, the flu, respiratory syncytial virus, and other infectious diseases,” Faustman said.

Some BCG-treated participants also received commercially available COVID-19 vaccines during the Phase III trial. The researchers observed that the Pfizer, Moderna, and Johnson & Johnson vaccines did not effectively protect people with type 1 diabetes against COVID-19. “Our study showed that the BCG vaccine neither increased the efficacy of the COVID-19 vaccine nor was it harmful to those who received the COVID-19 vaccine,” Faustman explained. “As the pandemic continues to evolve, it will be interesting to see if we can work with the FDA to allow access to the BCG vaccine for type 1 diabetics, who appear to be particularly at risk for all infectious diseases.”


This research suggests that the BCG vaccine, with its long-lasting protective effects, could be a valuable tool in the fight against infectious diseases, especially for vulnerable populations like those with type 1 diabetes. As we continue to navigate the challenges of the COVID-19 pandemic, such findings offer hope for more effective and enduring protection strategies.

For more science news stories check out our New Innovations section at The Brighter Side of News.


Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.


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