It's not easy to keep underfed women healthy while they toil through sittings and strut endless runways, all at the height of cold-and-flu season. "Everyone gets sick during Fashion Week," says 1 Models president Scott Lipps, whose agency reps Angela Lindvall and Helena Christensen. Enter John McDonald, the restaurateur behind Lever House and Lure Fishbar, who's now in the haute anti-sniffles business, too. He says he has spent the past two years developing E Boost, a slickly packaged powdered drink that contains vitamins B-12 and C, magnesium, zinc, potassium, and amino acids. How'd he get the right mix? "It was hilarious," says McDonald. "I would get white packets from the lab every day and pop them in water. We would see how many particles floated. We thought of adding ginseng, but it clumped.'' The product has been available for only two weeks, but he's distributed it via model agencies and at Grammy events; soon, it'll be aboard NetJets time-share planes and at W hotels. You know, the kinds of places where you simply couldn't pop a comparatively unchic Emergen-C.