I'm curious what they meant as well. Perhaps what they meant was the potential period where the virus is replicating in the body before the immune system detects it and kills it. I suppose even someone with the vaccine would have a very short-lived period of viral replication? Or perhaps they simply meant that humans could be fomites (eg, it gets on someone's hand, then they shake your hand, etc?)

Honestly I'm just guessing here. I suspect this is not a real concern.