Researchers at Washington University School of Medicine in St. Louis and the University of Texas Health Science Center in San Antonio recently found an HIV vaccine strategy that may be effective against this most common infection.

According to the Centers for Disease Control and Prevention, approximately 23.1 million people were living with HIV in 2014, and 10.2 million of them were HIV-positive. Currently there is no cure for HIV; however, one drug used to treat HIV prevents new infections for about 63 percent of patients.

Patients who receive antiretroviral drugs are considered HIV-positive because they have the virus, but it’s not growing at high levels in the blood. In this case, HIV grows in cells and only when it’s new and has not been exposed to a vaccine.

Several HIV vaccines have been tested over the last decade, but they are only partly effective, and it’s been unclear if antiretroviral drugs may blunt the immune response. In the new study, researchers used ritonavir, an HIV drug that is widely prescribed to treat cardiovascular disease, as a vaccination dose against HIV.

“We were able to immunize 40 of 42 HIV-infected study participants, with only minor lags in some patients,” said Alexander Yeh, an associate professor of infectious diseases. “This means that HIV vaccine strategies can be considered both for preventing new HIV infections and for reducing HIV-associated complications, including AIDS.”

Studies have shown that HIV antibodies induce an immune response, but HIV is not a virus that primarily infects and kills cells, so it’s unclear how this might impact the immune response to HIV vaccines.

“In HIV vaccine studies, it’s important to assess the duration and magnitude of the immune response,” Yeh said. “The results of our vaccine immunization study suggest that ritonavir can improve the immune response against HIV, because it does have immunogenic properties.”