Hoping to tackle the ongoing opioid crisis, scientists are hoping they’ll be able to start human trials of heroin and fentanyl vaccines as early as 2024. 

The vaccines are designed to protect people from accidental overdoses of heroin and its stronger, synthetic cousin, fentanyl. It works by prompting the body to produce fentanyl-specific antibodies that bind the drug in the blood and prevent it from entering the brain.

So far, it’s only been tested on rats and pigs, but their results suggested the vaccines could potentially offer a “safe, long-lasting, and prophylactic treatment” to combat opioid overdoses in humans too. 

“We anticipate testing our vaccines in humans in early 2024,” Dr Jay Evans, study author and director of the University of Montana's Center for Translational Medicine, said in a statement. 

“The human clinical trials will include a drug challenge to evaluate both safety and efficacy of the vaccines in early clinical development. We will also follow the patients to evaluate how long the antibodies against opioids will last,” he said.

“We start with the lowest dose – a dose that may not be effective,” Evans said. “Phase I clinical trials are focused on safety. When the first dose cohort is complete, a data safety monitoring board reviews the data and approves testing at the next dose level if the vaccine is safe. The process takes time until you reach dose levels that are both safe and effective,” added Evans. 

The vaccines in question will use toll-like receptors (TLR7/8) which typically play an important role in the immune response to viral infections. The team’s vaccine also utilizes the power of an adjuvant called INI-4001, which boosts the effectiveness of vaccines.

Speaking to IFLScience, Evans explained that the vaccines could provide immunity against an overdose for a number of years, although that still needs to be determined by their human trials.

"The duration of immunity in humans is speculative and will be determined as part of the Phase I/II clinical trials. The adjuvant we are using significantly boosts antibody titers and affinity in animal models and thus we anticipate the higher antibody titers will improve vaccine duration and durability. Based on data from other conjugate vaccines (pneumococcal vaccines) and the use of INI-4001 adjuvant we expect that durable immunity will last 2-4 years," he told IFLScience. 

He added: "Of course, this is speculative since both the vaccine and adjuvant have not been previously tested in people."

Scientists have dubbed the opioid epidemic “one of the worst public health disasters” currently affecting North America. Over the past two decades, fatal overdoses have been continually rising in the US and Canada, with 106,000 drug overdose deaths reported in 2021. Opioids, such as heroin and fentanyl, were involved in 80,411 overdose deaths in 2021.

There is no silver bullet for this problem. Along with complex social problems, many have argued the epidemic “represents a multi-system failure of regulation” driven by profit-hungry pharmaceutical companies. 

A safe and effective vaccine won’t solve the crisis, but it could save lives in the meantime. 

The results of the animal trial were published in the journal NPJ Vaccines.