A new HIV vaccine is now being tested in South Africa in a study that aims to enroll several thousand people, officials announced today.

The study is the first in seven years to test the effectiveness of a vaccine against HIV, said the National Institutes of Health (NIH), which is funding the study.

"If deployed alongside our current armory of proven HIV-prevention tools, a safe and effective vaccine could be the final nail in the coffin for HIV," Dr. Anthony Fauci, director of the NIH's National Institute of Allergy and Infectious Diseases, said in a statement. "Even a moderately effective vaccine would significantly decrease the burden of HIV disease over time in countries and populations with high rates of HIV infection."

In South Africa, more than 1,000 people contract HIV each day, the NIH said.

The last HIV vaccine to show promise was tested in Thailand starting in 2003. In 2009, researchers from that study announced that the vaccine was 31 percent effective at preventing HIV infection over 3.5 years.In other words, the rate of infection was 31 percent lower in the group that got the vaccine, compared to the group that got a placebo.

The new South African study will use an HIV vaccine that is similar to the one used in the Thai study but that has been modified to provide greater and longer-lasting protection, the researchers said.

The researchers want to enroll 5,400 sexually active men and women ages 18 to 35 who do not have HIV, and results are expected in 2020, the NIH said.

"HIV has taken a devastating toll in South Africa, but now we begin a scientific exploration that could hold great promise for our country," study researcher Glenda Gray, president and chief executive officer of the South African Medical Research Council, said in a statement. [27 Devastating Infectious Diseases]

In the Thai study, researchers used two vaccines: one called ALVAC-HIV, which consisted of a bird virus that had been modified to contain three HIV genes, and another vaccine called a protein subunit vaccine, which contained a genetically engineered version of a protein found on the surface of HIV.

The South African study will use these two vaccines, but with some key changes. Both vaccines in the new study have been modified to protect against a subtype the virus known as HIV subtype C, which is found in especially high numbers in South Africa. In addition, the protein subunit vaccine used in the new study will contain a different adjuvant (an ingredient added to a vaccine to boost its effects) than the one used in the Thai study. And the South African study will include a booster shot after one year, with the hopes of prolonging the protective effect, the researchers said.

Participants in the new study will be randomly assigned to receive either the study vaccines or a placebo. If any participants become infected with HIV, they will be referred to local medical staff for care, and will be counseled on how to reduce their risk of transmitting HIV, the NIH said.

Sanofi Pasteur will supply the ALVAC-HIV vaccine, and GlaxoSmithKline will provide the protein subunit vaccine.

Original article on Live Science.