[agnokapathetic]

mRNA vaccines are about getting mRNA into just a few non-specific cells which then instructs the cell to produce Corona Virus Spike Protein. This gets identified by the immune system which then makes antibodies targeting the spike protein.

So the mRNA only needs to get taken up by a few cells to produce an immune response.

The HIV CRISPR-Cas technique needs to target several orders of magnitude more cells in the body, and is performing a far more complicated procedure than simple transcription like with an mRNA vaccine.