U.S. President Joe Biden received an updated COVID-19 booster shot on Tuesday afternoon.
"This virus is constantly changing," Biden said at the Eisenhower Executive Office Building near the White House. "New variants have emerged here in the U.S. and around the world."
"Your old vaccine or your previous COVID infection will not give you maximum protection," he warned.
More than 20 million Americans have received updated COVID-19 vaccine so far, according to the White House.
"Not enough people are getting it," Biden stressed. "The weather is getting colder. People will spend more time indoors. And contagious viruses, like COVID, are going to spread considerably more easily."
The United States has reported 97 million COVID-19 cases, along with more than 1 million deaths, according to data from Johns Hopkins University.
Nearly 400 people are still dying each day from the virus in the country. Biden said, "that number is likely to rise this winter."
The United States "could be facing another very dark pandemic winter," warned Martha Lincoln, assistant professor of medical and cultural anthropology at San Francisco State University, and Nate Holdren, who teaches at Drake University, in a joint opinion published by Time recently.
The U.S. government's "failure to push for better pandemic measures will cost the lives and health of many Americans," they wrote.