A century-old tuberculosis vaccine reduced insulin use in people with diabetes, new clinical trial results suggest. The catch: Research on this vaccine has divided the diabetes research community for years.

The Bacillus Calmette-Guérin (BCG) vaccine contains a weakened version of the bacterium Mycobacterium bovis, the germ that causes tuberculosis. Inside the body, the vaccine prompts a protective response against the bacterium. It’s also approved to treat bladder cancer, acting as an immunotherapy that rouses an attack against tumors. The leader of the trials, Dr. Denise Faustman of Massachusetts General Hospital, has long been the subject of controversy. Early on, critics argued that she falsely raised hope that her work could lead to a cure for those with long-standing type 1 diabetes.

Faustman and colleagues presented results from two new clinical trials at the annual meeting of the American Diabetes Association in New Orleans. The results suggest the BCG vaccine may offer benefits to people with type 1 diabetes — not by curing the disease, but by improving blood sugar control or slowing the disease’s progression, depending on the population. Here’s what to know.

About 2 million Americans have type 1 diabetes, an autoimmune disease that destroys insulin-making cells in the pancreas. Patients monitor their blood sugar and inject insulin multiple times a day, carefully calculating every dose. Too much insulin and blood sugar crashes, causing shakiness, seizures or blackouts; too little, and chronically high blood sugar damages the heart, kidneys, eyes and nerves.

Early in the disease process, patients still have some insulin-making cells, but people with longstanding disease have almost none left. Curing type 1 diabetes in those with longstanding disease is a tough problem that requires stopping the immune attack and regenerating enough insulin-making cells to eliminate the need for injected insulin. The new trial results do not show that level of improvement. However, “the new data suggests that BCG could reduce insulin resistance and decrease the amount of insulin needed in patients with both late-onset and juvenile-onset type 1 diabetes,” said Dr. Gillian Goddard, a board-certified endocrinologist at NYU Langone Health who wasn’t involved in the studies.

“These are phase 2 trials so further trials will be needed to fully understand the benefits of BCG in Type 1 diabetes,” she told Live Science in an email, “but it could be another tool in our arsenal for improving the lives of patients with type 1 diabetes.”

Others are more skeptical. Dr. John Buse, an endocrinologist at the University of North Carolina School of Medicine, cautioned that the improvements seen in these small trials may not hold up in a larger trial. The history of type 1 diabetes research “is littered with losers and no blockbuster successes,” he told Live Science in an email.