Unfortunately for us governments that have strong vaccine...

Unfortunately for us governments that have strong vaccine mandates and have encouraged herd immunity have made it clear to spl that running a preventative trial would be a waste of money. Viraleze would not be approved to be marketed as a preventative. Even if results from a well designed trial had enough statistical power to prove statistically significant results and was able to meet all endpoints, representations for Covid would not be allowed.
I suspect that that public health advice will change in the future. Representations for prevention could be made to control the next pandemic whilst suitable vaccines were manufactured. I imagine spl will conduct a proper prevention trial at some stage.