The C.D.C. warns Americans not to travel for the holidays and outlines ways to shorten quarantine times.

The C.D.C. warns Americans not to travel for the holidays and outlines ways to shorten quarantine times.

Citing the spiraling rise in coronavirus cases nationwide, the Centers for Disease Control and Prevention on Wednesday warned Americans not to travel over the holidays, and outlined two ways to shorten the recommended quarantine times for people who may have been exposed to the coronavirus, especially those who may choose to travel anyway.

“The best thing for Americans to do during the holiday season is to stay at home and not travel,” said Dr. Henry Walke, who oversees day to day management of pandemic response for the agency.

The guidance came as the C.D.C. director, Dr. Robert Redfield, also warned on Wednesday that the nation faces a devastating winter, predicting that total deaths from Covid-19 could reach “close to 450,000” by February unless a large percentage of Americans follow precautions like mask-wearing.

“The reality is, December and January and February are going to be rough times,’ said Dr. Robert Redfield, the head of the C.D.C., in an address to the Chamber of Commerce Foundation. “I actually believe they’re going to be the most difficult time in the public health history of this nation.”

Previously, the C.D.C. had recommended a 14-day quarantine period following potential exposure, and officials said they still supported the longer period as the safest option. But officials also recommended two alternatives.

Those without symptoms may end quarantine after seven days, followed by a negative test for the virus, or after 10 days without a negative test, agency officials said at a news briefing. P.C.R. or rapid tests are acceptable, the agency said, and should be taken within 48 hours of the end of the quarantine period.

“We can safely reduce the length of quarantine, but accepting that there is a small residual risk that a person who is leaving quarantine early could transmit to someone else if they became infected,” said Dr. John Brooks, the C.D.C.’s chief medical officer for the Covid-19 response.

(Quarantine refers to people who are well but may become ill; isolation refers to those known to be ill.)

Agency officials also recommended that Americans who are traveling get tested for the infection one to three days before the trip and again three to five days after returning. Returnees should eliminate nonessential activities for seven days. ...