Century-old vaccine shields type 1 diabetics from infections

Recent studies conducted by researchers at Massachusetts General Hospital (MGH) have demonstrated that the Bacillus Calmette-Guérin (BCG) vaccine, originally developed for tuberculosis, offers significant protection against severe COVID-19 and other infections in individuals with type 1 diabetes. These findings emerged from two randomized, double-blind, placebo-controlled trials during the COVID-19 pandemic.

Vaccine Effectiveness in Type 1 Diabetics

Individuals with type 1 diabetes are particularly vulnerable to infections, including COVID-19, often experiencing worse outcomes than the general population. According to Denise Faustman, MD, PhD, senior author of the study and director of MGH’s Immunobiology Laboratory, existing COVID-19 vaccines have shown limited efficacy in this group. However, the BCG vaccine appears to offer considerable protection against both COVID-19 and other infectious diseases.

Phase II and III Trials

Two separate trials were conducted to evaluate the BCG vaccine’s effectiveness. The Phase III trial, detailed in iScience, took place during the latter stages of the U.S. pandemic when the Omicron variant was prevalent. An earlier Phase II trial, whose results were published in Cell Reports Medicine, was conducted during the early pandemic phase.

Internationally, several studies examined whether a single BCG booster shot could protect previously vaccinated adults from COVID-19, yielding mixed results. The MGH trials, however, were distinct. Participants received multiple doses (five or six) of a highly potent BCG strain and were monitored for 36 months, a substantially longer period than other studies.

Study Findings

Participants in the MGH trials had never previously received the BCG vaccine, nor had they been exposed to tuberculosis, making these trials unique. A total of 141 individuals with type 1 diabetes participated: 93 were administered multiple doses of the BCG vaccine, while 48 received a placebo. The study spanned various COVID-19 genetic variants and other infectious diseases over 36 months.

In the Phase II trial, conducted from January 2020 to April 2021, the BCG vaccine showed an efficacy rate of 92% against severe COVID-19, comparable to the effectiveness of Pfizer and Moderna vaccines in healthy adults. Over the entire pandemic period, the BCG vaccine maintained a significant efficacy rate of 54.3%. Additionally, participants treated with BCG experienced fewer viral, bacterial, and fungal infections.

Implications for Long-Term Immunity

The BCG vaccine's ability to confer long-lasting immunity is particularly noteworthy. Unlike COVID-19 vaccines, whose effectiveness wanes after a few months, the BCG vaccine offers the potential for prolonged protection, possibly spanning decades. This could extend to various infectious diseases beyond COVID-19, including influenza and respiratory syncytial virus.

Combination with Other COVID-19 Vaccines

Some trial participants also received commercial COVID-19 vaccines (Pfizer, Moderna, Johnson & Johnson). The study found that these vaccines did not enhance efficacy for type 1 diabetics when combined with the BCG vaccine, nor did they adversely affect those who received them.

Future Prospects

As the pandemic evolves, researchers hope to collaborate with the FDA to make the BCG vaccine accessible to type 1 diabetics, who are at higher risk for severe infections. This research highlights the potential of the BCG vaccine as a versatile tool in the fight against infectious diseases, providing a promising avenue for enhancing public health.

The research was funded by The Iacocca Foundation, Boston, MA, and involved contributions from various MGH scientists, including Willem M. Kühtreiber, Emma R. Hostetter, Grace E. Wolfe, and others.

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