Study looks at BCG vaccine, COVID protection for type 1 diabetics

Harvard Medical School

This article is part of Harvard Medical School’s continuing coverage of COVID-19.


Researchers at Harvard Medical School and Massachusetts General Hospital have published a new paper in Cell Reports Medicine demonstrating the protective potential of multiple doses of the bacillus Calmette-Guerin (BCG) tuberculosis vaccine against COVID-19 and other infectious diseases.

In a double-blind, placebo-controlled study of patients with type 1 diabetes conducted at the start of the pandemic, before COVID-specific vaccines were available, the researchers found that 12.5 percent of placebo-treated individuals and 1 percent of BCG-treated individuals met criteria for confirmed COVID-19, yielding a vaccine effectiveness of 92 percent.

The BCG-vaccinated group also displayed protective effects against other infectious diseases, including fewer symptoms, lesser severity and fewer infectious disease events per patient. No BCG-related systemic adverse events occurred.

BCG’s broad-based infection protection suggests that, in addition to current SARS-CoV-2 variants, it may potentially provide protection against new SARS-CoV-2 variants and other pathogens.

The researchers are hoping the results will spur a larger scale study of the effects of the BCG vaccine in patients with type 1 diabetes, considered among the most vulnerable groups at risk for severe COVID-19.

Tuberculosis strain

The BCG vaccine is an avirulent tuberculosis strain of Mycobacterium bovis, historically given to protect against tuberculosis and, since its introduction in 1921, has been the most widely administered vaccine in the history of medicine.

Considered extremely safe, BCG is on the World Health Organization’s list of essential medicines and is given to roughly 100 million children per year globally.

BCG is also one of the most affordable medicines, costing less than a dollar a dose in many parts of the world.

“Multiple studies have shown that adults with type 1 diabetes who are diagnosed with COVID-19 are at increased risk of severe illness. We found that three doses of BCG administered prior to the start of the pandemic prevented infection and limited severe symptoms from COVID-19 and other infectious diseases,” said Denise Faustman, HMS associate professor of medicine and director of the immunobiology laboratory at Mass General.

“Unlike the antigen-specific vaccines currently in use to prevent COVID-19, BCG’s mechanism of action is not limited to a specific virus or infection,” she said.

The participants in the COVID trial had previously enrolled in a clinical trial testing the effectiveness of the BCG vaccine for type 1 diabetes. Participants in the test group had received multiple vaccinations before the onset of the pandemic in early 2020.

“This data set is unique and exciting because the patients were all vaccinated with multiple doses of BCG prior to the onset of the epidemic. Prior to the trial they had no known exposure to tuberculosis or prior BCG vaccination. This eliminates the major confounding factors that have limited other trials,” said Hazel Dockrell, a London School of Hygiene & Tropical Medicine infectious diseases expert who was not officially involved in the study.

“The results support the idea that BCG needs time to have a clinical effect, but its effects may then be very lasting and durable,” Dockrell said.

The 144 adults with type 1 diabetes (96 BGC-treated and 48 placebo) analyzed in the COVID-19 trial were part of an ongoing phase 2b clinical trial testing BCG as a treatment for adults with established type 1 diabetes. Patients were followed for COVID-19 related outcomes for 15 months.

Outcomes for the COVID-19 trial included COVID-19 infection rate, COVID-19 related symptoms, reduction of overall infectious disease symptoms and SARS-CoV-2 antibody-level presence and intensity.

The type 1 diabetes outcomes were not unblinded as part of this study and will be unblinded at the completion of the trial in 2023.

Adapted from an Mass General news release.

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