Researchers at the Harvard-affiliated Beth Israel Deaconess Medical Center recently developed a vaccine for rhesus monkeys that provides immunity against the Simian Immunodeficiency Virus (SIV), a virus found in monkeys that is analogous to HIV.

Rhesus monkeys that received this new vaccine had an 80 percent reduction in their chance of acquiring SIV upon future exposures, according to Dan H. Barouch, the lead author of the study and a professor at Harvard Medical School.

In addition, the monkeys who still contracted an SIV infection after vaccination had a lower SIV viral count in their blood compared to unvaccinated monkeys who acquired an infection.

According to Barouch, this new vaccine is a breakthrough because “three HIV vaccine concepts have been tested in [the past] 30 years—and of those, two failed and one showed only a marginal improvement.”

SIV and HIV vaccines have been difficult to create for years because common methods of vaccine development have proven unsuccessful in providing full effective immunity.

Barouch’s vaccine uses a non-conventional “prime-boost vaccine combination,” which requires the subject to have two injections. Each injection contains a harmless vector virus that safely transports weakened SIV virus particles into rhesus monkey cells. Once transported, these SIV particles then trigger a controlled immune response and allow the subject to develop immunity against future infections.

Barouch said he believes that it is this particular combination of viral vectors that allows protective immunity, in contrast to previous unsuccessful vaccination attempts.

While most vaccine developers work with weaker strains of SIV virus, Barouch said this vaccine was particularly promising because his team was able to develop the vaccine successfully with more potent strains of SIV.

“There are many different SIVs,” Barouch said. “Some are wimpy and some are hot. We used a difficult-to-neutralize strain and got these results.”

While Barouch said he is not yet certain when initial human vaccine trials will begin, he added that he is optimistic for future work.

“This gives two major advances: an understanding of what immune response is or how it is wired for protection, and a human clinical trial option.”

—Staff writer Armaghan N. Behlum can be reached at behlum@college.harvard.edu.