Around 3,800 men who have sex with men will be part of Johnson & Johnson's historic vaccine trial.

Trials on a potential HIV vaccine will begin later this year in the United States and Europe, according to a Bloomberg interview with Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases.

Johnson & Johnson is leading the immunization effort, where approximately 3,800 men who have sex with men will be administered six shots over four sessions. The potential vaccine aims to target multiple strains of HIV, which mutates quickly in the human body. Johnson & Johnson's potential vaccine has proven effective in about two-thirds of animals. No harm was found in humans who've already been administered the drug.

Meanwhile, another potential vaccine began tests in 2017 on about 2,600 African women. Health officials believe having both trials — held in different parts of the world and on different demographics — can lead to quicker approvals for public use should they demonstrate success.

Even though pre-exposure prophylaxis, or PrEP, is known to halt nearly all HIV transmissions, its high cost leaves it out of reach for many without means or access, especially those in developing countries. Daily adherence is also a big factor when it comes to PrEP's effectiveness.

“The cost of treating HIV patients — the burden for patients, the burden for society — is very high,” Paul Stoffels, Johnson & Johnson's chief scientific officer, told Bloomberg.

Fauci and Johnson & Johnson are expected to release more information later this month on the U.S. and European trials.