Sherlock's shoulder stings, the pain gnawing at him and slowly getting worse. He doesn't complain, simply bears it out and doesn't mention it to John. No use in worrying him unnecessarily, and it isn't a serious wound, though he is getting to feel just slightly feverish. (It has a long way to go before it becomes serious, and he takes comfort in that knowledge.)
John, however, knows well that Sherlock's injured. He sees the faint gloss to his eyes, the way they become starry under the street lamps, the minutely different angle at which he holds his arm, but he won't press for details (not yet, at least), instead reassures himself with the knowledge that if it were serious then Sherlock wouldn't be able to hide it. (Not that he's doing very well as it is, but that's beside the point.)
All the same, John takes out the next three slayers that they come across, Sherlock only putting up a token resistance against his insistence. He briefly considers hauling Sherlock back to Baker Street anyway, but shakes the thought off. It can't be that serious of an injury, and though there also can't be too many slayers left, he doesn't much like the thought of leaving the others to deal with them. (He knows this is the sort of loyalty that almost got him killed in Korea, but the others are his family too and he can't do that to them.) Besides, Sherlock would never forgive him for it, and never is a long time for vampires.
Instead, after a lucky escape from a slayer with a long bow, he binds Sherlock's shoulder with part of his own shirt, cursing himself for not bringing any of Mrs Hudson's herbs, and the two carry on, flakes of snow drifting melancholically to the ground. A light dusting over boots and concrete, and spilled blood.