Sex and drugs are not to blame for high rates of hepatitis C virus (HCV) among baby boomers, according to a new stigma-busting study published in The Lancet, which suggests the epidemic is more likely the result of modern medicine’s evolution rather than risky behavior, Hepatitis Central reports.

Today, baby boomers (those born between 1945 and 1965) constitute up to 75 percent of the more than 6 million people estimated to be living with a chronic hepatitis C infection in North America. Past research has linked the epidemic in this generation to an uptick in injection drug use in the 1960s. However, according to new genetic timelines, the hepatitis C epidemic actually hit its peak much earlier than the “sex and drugs revolution.”

For this new study, researchers in Vancouver examined the phylogenetic sequences of more than 40,000 cases of hepatitis C genotype 1a (the most dominant virus strain) in North America. Through these DNA markers, they determined that hepatitis C saw its greatest infection rates between 1940 and 1965, with the epidemic stabilizing around 1960—15 years earlier than previously thought.

The new timeline points to unsafe medical procedures conducted during World War II and its aftermath as the main cause of hepatitis C’s spread during this time, not risky behavior. To support this theory, study authors noted that between 1945 and 1960, there was a massive increase in the number of medical procedures conducted in the United States, at a time when blood transfusion technologies were still in their infancy.

What’s more, prior to 1950, injections were given in glass and metal syringes, which medical staff commonly reused well into the 1960s. Experts said improper or incomplete sterilization in crowded settings could have easily transmitted blood-borne pathogens like hepatitis C to the baby boomer population.

By spreading this information, researchers hope to help destigmatize hepatitis C among baby boomers and encourage more people to access HCV testing and treatment.