Perhaps this could be a beneficial prophylaxis. And having another treatment that uses CRISPR to remove the provirus is also an essential to have a durable cure for patients already infected. https://www.bbc.com/news/health-68609297
Look up EBT 101. Human trials started last year for a CRISPR based cure for HIV. This is from the same team that was able to cure SIV in monkeys using the same technique.
My layman, super naive understanding is that an HIV vaccine could also help an HIV-positive person (with a well-managed HIV infection), because it dampens transmission from infected to uninfected cells.
