Regular monitoring throughout the eight-year study found that HbA1c levels of individuals receiving the vaccine dropped by more than 10 percent at the three-year mark and by more than 18 percent after four years of treatment. These levels reached near-normal figures five years after treatment.
HbA1c refers to glycated hemoglobin, which develops when hemoglobin, the red blood cell protein that carries oxygen throughout the body, is combined with glucose in the blood.
Participants treated with BCG were found to have an average HbA1c of 6.65 four years later. The threshold for diabetes diagnosis is close to an HbA1c of 6.5.
Researchers saw a delay in the results of a previous BCG study from Italy, so they revisited their own study, WBUR reported.
“The secret of [those] trials was that the drug took a while to kick in,” she said. “That gave us a pretty good clue that the time course for this drug […] was different than we originally knew,” Faustman said.
Individuals in that near normal range have dramatically reduced risk of associated complications, such as renal disease, heart disease and blindness.
The vaccine, according to the researchers, helps the body boost production of tumor necrosis factor, a hormone especially beneficial to Type 1 diabetics.
In 2001, Faustman's team first reported that inducing TNF production may cure Type 1 diabetes in mice, "but since TNF dosing is toxic in humans, clinical trials have utilized BCG for its ability to elevate TNF levels safely," Medical Xpress reported.
The MGH researchers also noted that BCG may reduce blood sugar elevations in mice caused by non-autoimmune attacks. This raises the possibility that the vaccines may even be beneficial against Type 2 diabetes.
Faustman is also expected to present five-year follow-up results of a separate group of BCG clinical trial participants at the 78th Scientific Sessions of the American Diabetes Association in Orlando, Florida on Saturday, June 23.
The researchers plan to replicate these findings with another trial currently underway.
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Approximately 1.25 million American children and adults have Type 1 diabetes, according to the American Diabetes Association.
In Type 1 diabetes, the insulin-producing beta cells of the pancreas are "mistakenly attacked and destroyed by the immune system," according to Medical News Today.
And in Type 2, the most common category of diabetes accounting for 90-95 percent of all cases, the body’s cells either stop responding to insulin or the beta cells can’t produce enough of the hormone.
People suffering from either type of the disease have blood sugar levels that can become too high. This condition is called hyperglycemia and can lead to kidney disease, heart disease and more if it's not properly controlled or treated.