This week, the biotech company Moderna will start human trials for its HIV vaccine. Its HIV vaccine will be the first of its kind to use messenger RNA (mRNA), an approach that Moderna used in its effective COVID-19 vaccine. The clinical trials will start on August 19 and end sometime around spring 2023, according to the National Institutes of Health’s trial registry. They will involve 56 HIV-negative participants aged 18 to 56. The participants will be given one or two forms of mRNA that cause the body to form defenses against HIV infection. In the past, HIV vaccines used inactivated forms of the virus. However, previous trials showed that these forms didn’t produce any immune responses. In fact, researchers canceled one trial in Thailand during the 2000s after inactivated forms of the virus were found to actually increase people’s risk of catching HIV rather than preventing infections.