Get vaccinated, get your booster shots, and prepare for a grim winter ahead if you defy official instructions. That is the message President Joe Biden will deliver Tuesday when he addresses the nation on the latest government plan to counter the surging coronavirus omicron variant. White House press secretary Jen Psaki on Saturday previewed the pre-Christmas speech on Twitter, noting a “stark warning” for unvaccinated Americans is coming. She said the president will announce new steps his administration is taking “to help communities in need of assistance.