What is the fine-grained topic of the following text: Now J&J is stepping forward and spearheading the first efficacy study — HVTN 705/HPX2008, also known as “Imbokodo” — of a new, so-called mosaic vaccine that is enrolling 2,600 African women to check on its ability to quell the spread of the lethal virus. Only return the topic.
Efficacy study of J&J's mosaic vaccine against a lethal virus