As concern grows in Colorado over the spread of the coronavirus’s delta variant, a number of metro Denver hospitality businesses have begun requiring proof of vaccination from patrons seeking entry into dining rooms, bars and concert halls. But for now, at least, there doesn’t seem to be a groundswell of support among Denver restaurateurs for such measures as many watch and wait for government guidance or backing. “It comes down to this,” said Dakota Soifer, owner of Boulder’s Café Aion, which will begin requiring proof of vaccination next week.