US President Joe Biden warned on Thursday that the Omicron variant of the coronavirus is going to spread more rapidly in the United States and that a winter of severe illness and death awaits the unvaccinated.

Getting an update on the pandemic from top health advisers, Biden also said it is past time for people to get booster shots and urged them to do so as quickly as possible.

“We are looking at a winter of severe illness and death” for the unvaccinated, Biden said. At least 36 states have reported confirmed Omicron cases, officials from the Centers for Disease Control said on Wednesday.

“If you’re vaccinated and have your booster shot, you’re protected from severe illness and death,” Biden said.

Biden said the Omicron variant had not spread as fast in the United States as it could have thanks to his administration’s policies. “It’s here now. It is spreading and it’s going to increase.”

“Get your booster shot. It’s critically important,” he said.