It seems in this article it inhibits expression of the virus, not the injection stage. As far as photoactivity goes...
I think it's just a matter of the molecules in question being cleaved, by photons, into the effective particles. Kind of an oxidation reaction that creates free radicals that preferentially attack the target you are looking for. In this case some phase of viral reproduction.
That's how my rudimentary understanding of it goes. Perhaps someone with more understanding will chime in.
All these posts are on behalf of Stimpy, my yellow bullhead. He is an adventurous fish, and I feel his exploits are worth sharing...so much so, I occasionally forget that HE is the one who does these things. Sometimes I get caught in the moment and write of his experiences in the first person; this is a mistake, for I am an upstanding citizen who never does wrong. Stimpy is the degenerate.