BRUSSELS – Please leave a chair empty at this year's family Christmas dinner as a precaution, or face the possibility of having that chair empty forever.That's the stark dilemma Belgium's prime minister has set to urge smaller festive family gatherings, as Europeans battle with containing the surging COVID-19 pandemic over the holiday season.Alexander De Croo argued that the country's long-running, costly efforts should not be thrown away for the sake of a few warm and fuzzy hours exchanging gifts under the Christmas tree. “I would not want the progress of the past four weeks to be wasted because of four days,” he told legislators this week.