I'm familiar with "Infizierte" being used to refer to infected person(s), so you can use it as a verb like this: "Ich hoffe die haben einander auf der Demo nicht infiziert"?
Yes, you can. In this context, it means the same, but note two things:
- infizieren, in contrast to anstecken, has a rather "professional" or formal sound to it. It is usually used more in scientific contexts, or when people want to sound educated. Anstecken does not have such connotation and can be used in elaborate language as well as in colloquial one. (Altough nowadays it leaks into everyday language, of course.)
- Both infizieren and anstecken are, I feel, much more often used in the reflexive construction sich anstecken; this expresses the aspect of involuntary contact ("getting infected"), while the transitive jemanden/einander anstecken has a certain volitionary ring to it. It does not need to express "to infect someone on purpose", but does sound like that much more than the English form (since you don't have the reflexive there).
Ich hoffe, die haben sich auf der Demo nicht infiziert.
will express the same thing a bit more naturally, unless you want to emphasize the transitive aspect.