evidence: Overcoming challenges "HIV has many tricks up its sleeve, making it hard to develop an effective vaccine using standard methods," explained Marovich. "As one of the fastest-mutating viruses, HIV has millions of variants. By comparison, the number of SARS-CoV-2 variants of concern or variants of interest causing the COVID-19 pandemic is about a dozen [as of December 2022]." [...] NIH Launches Clinical Trial of Three mRNA HIV Vaccines - NIAID is supporting some of the first human tests of HIV vaccines based on mRNA technology.