This statement makes no sense.

The mRNA vaccines are sterile; there's no active virus or bacteria in them. It's also conclusively determined they reduce transmission.

(The sterility of a vaccine has no impact on its ability to reduce transmission, anyways; they're not linked. Live-virus vaccines like the flu nasal spray vaccine can still prevent disease.)

I think the comment was alluding to 'sterilizing immunity', rather than the aseptic nature of the vaccines themselves.