U.S.-backed researchers are getting closer to a vaccine that could prevent people from getting infected with the human immunodeficiency virus (HIV), offering hope for millions around the world.

People in their 20s who contract the virus today can expect to live an additional 53 years, on average, and may never develop AIDS, thanks to the numerous types of antiretroviral treatments in use. In the early 1980s, the average life expectancy for someone with HIV who developed AIDS was 1-2 years.

"The success of therapies and treatments [in containing the disease] is nothing short of breathtaking," says Dr. Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases. But while treatments work to extend the lives of people living with HIV, unfortunately about 1.8 million people contracted the virus in 2016, according to the United Nations.

Two trials underway

Fauci described two clinical trials underway in South Africa - funded, in part, by the U.S. National Institute of Health (NIH) - that may lead to a vaccine that stops new infections of HIV.

One study, "Imbokodo," aims to enroll 2,600 women in sub-Saharan Africa to help assess the trial vaccine's safety and effectiveness. "Imbokodo" is the Zulu word for "rock," which refers to the strength of women and their importance in the community.

The Imbokodo trial, led by the New Jersey-based company Johnson & Johnson, hopes to eventually expand to Malawi, Mozambique, Zambia and Zimbabwe. Researchers expect results in 2021.

Another study is exploring an updated version of an experimental vaccine that showed promise in Thailand. Scientists anticipate results in late 2020.

Both trials "represent science's current best efforts to develop a vaccine to prevent HIV infection," Kathy Mngadi of the Centre for the AIDS Programme of Research in South Africa said in a statement. "We are grateful to the people of southern Africa who volunteer for these trials, and the communities in which the trials are conducted to help develop what could be a true game-changer for the HIV/AIDS pandemic." The South African Medical Research Council is helping implement the study in South Africa.

Historically, the search for an HIV vaccine has been challenging, due in part to the unique properties of the virus, including its ability to mutate rapidly and its global genetic diversity, with multiple strains and subtypes prevalent in different parts of the world, according to Johnson & Johnson.

Why treatment still matters

Fauci said a vaccine will take time to develop, and he warned against becoming complacent about HIV/AIDS. "Despite all the scientific progress [in treating and preventing HIV] we have serious implementation gaps," he said. Fauci noted that 30 percent of newly infected people don't know they're infected, and 60 percent are not getting adequate treatment. "We could essentially end the epidemic with improved implementation... we can't yet take our foot off the gas."