The company roped in Winfrey as its public face in October, in a bid to use her popularity to lift subscription numbers and reverse a nearly three-year decline in sales. The former TV talk-show star sparked interest in Weight Watchers by hosting a conference call with its members and tweeting about her weight loss under a company program. It is too early to judge Winfrey’s impact on driving sales, S&P Global Market Intelligence analyst Efraim Levy said, adding he expected the stock and earnings to be volatile.