Depends how thinly spread out the material is. If there were clumps or mounds of material, who knows how long the center part could remain infectious?

And what happened during the interim time before the sidewalk was finally cleaned? Was someone guarding it until then? Did someone's dog lick the vomit and then go home and lick their owner on the face shortly thereafter? Did a child innocently ride their bike through it and then somehow touched their tire later with an unprotected hand? These are hypotheticals, of course, but not unreasonable scenarios, I think.

Which just means that someone in charge should have thought about the infection risk pretty early on. It's no secret that he vomited outside when moving to the ambulance because it was widely reported.