Researchers at the University of Minnesota are getting closer to clinical trials of a vaccine for opioid addiction.

Three studies published in the past six months show incremental success, including one in the Journal of Pharmacology and Experimental Therapeutics that demonstrated that a vaccine could prevent oxycodone and heroin opioid molecules from reaching the brain.

"We are getting closer," said Marco Pravetoni, the lead researcher who has been studying a vaccine to treat addiction for 10 years.

A vaccine to confront addiction might sound unusual, but it would work like any vaccine by stimulating the immune system to produce antibodies. Instead of targeting influenza or poliovirus, the antibodies would be coaxed to bind to opioid molecules and prevent them from crossing the bloodstream barrier to the brain.

If successful, this approach would prevent or reduce the euphoric and addictive effects of opioids, but also the therapeutic and painkilling benefits. As a result, the vaccine would likely need to be reserved for people with known addictions, said Pravetoni of the Department of Pharmacology. "There are ethical concerns to immunizing people preventively for something like drug abuse."

The vaccine also would be administered periodically — more like a seasonal flu shot than a pediatric series.

Another challenge has been developing the vaccine in a way that inhibits certain opioids, but permits opioid treatment drugs such as methadone and buprenorphine to work.

In Minnesota, there has been a sixfold increase in deaths in the past 20 years from the misuse and abuse of opioids — both illicit forms such as heroin and prescription painkillers such as oxycodone.

Recent increases in federal funding and focus on the opioid epidemic could expedite vaccine development. Pravetoni said he expects he will soon seek additional federal funding for clinical trials.

"Its going to take a while before its going to be out there and available to the public," he said. "That's my cautionary statement. We really believe in this, but it's not going to be ready tomorrow."