Faced with a seemingly unstoppable surge in coronavirus infections, officials at the Centers for Disease Control and Prevention on Thursday urged Americans to avoid travel for Thanksgiving and to celebrate only with members of their immediate households — a message sharply at odds with a White House eager to downplay the threat.
The plea, delivered at the first C.D.C. news briefing in months, arrived as many Americans were packing their bags for one of the most heavily traveled weeks of the year. It is the first time that the agency has warned people away from traditional holiday celebrations.
“The safest way to celebrate Thanksgiving this year is at home with members of your household,” said Erin Sauber-Schatz, who leads the agency’s community intervention and critical population task force. She urged Americans to reassess plans for the coming week.
The C.D.C.’s warning runs counter to messages from administration officials, who have denounced concerns that Thanksgiving celebrations will speed the virus’s spread.
“A lot of the guidelines you’re seeing are Orwellian,” Kayleigh McEnany, the White House press secretary, said on “Fox & Friends,” singling out a requirement in Oregon that gatherings not exceed more than six people.
Members of the White House coronavirus task force did not even mention Thanksgiving at a news conference on Thursday, even as they warned of the hazards associated with indoor gatherings and urged “vigilance” in the face of rampant infections.
Earlier in the week, Dr. Scott Atlas, a scientific adviser to President Trump, mocked the idea that older relatives would be put at risk over the holiday weekend, although there is ample medical evidence that seniors are much more likely to become ill if they are exposed to the virus and to die if they become sick.
“This kind of isolation is one of the unspoken tragedies of the elderly, who are now being told, ‘Don’t see your family at Thanksgiving,’” Dr. Atlas said. “For many people, this is their final Thanksgiving, believe it or not.”
An estimated 55 million Americans had planned to travel for the holiday, according to AAA Travel. But rising coronavirus infections, new quarantine rules and increased unemployment have combined to deter travelers in the past few weeks, and that number will be at least 10 percent lower now, the largest year-over-year decrease since 2008.
United Airlines said recently that it expected Thanksgiving week to be its busiest period since the pandemic’s onset. But on Thursday, the airline reported that bookings had slowed and cancellations had risen. American Airlines has slashed flights between the United States and Europe as cases rise sharply on both sides of the Atlantic.
Emboldened C.D.C. officials, rarely heard from in recent months, have been speaking more forcefully since President-elect Joseph R. Biden Jr. won the election. On Thursday, agency researchers said they were alarmed by the “exponential” rise in coronavirus infections, hospitalizations and deaths across the country.
More than one million new cases have been reported in the past week alone.
“Amid this critical phase, the C.D.C. is recommending against travel during the Thanksgiving period,” Dr. Henry Walke, Covid-19 incident manager at the agency, said at a news briefing. “All Americans want to do what they can to protect their loved ones.”
As of Wednesday, the seven-day average of daily new cases across the country had surpassed 162,000, an increase of 77 percent from the figure two weeks earlier. More than 79,000 hospitalizations were reported on Wednesday.
Officials in California on Thursday announced a curfew aimed at trying to quickly curb a surge of new coronavirus infections. Nearly all of the residents of the nation’s most populous state will be barred from leaving their homes to do nonessential work or to gather from 10 p.m. to 5 a.m.
Gov. Gavin Newsom’s order comes amid what state officials and experts have described as an alarming — but not yet irreversible — wave of new infections heading into a dangerous Thanksgiving week.
Given the growing crisis, the C.D.C.’s timing confounded some scientists who have warned for weeks that the holiday gatherings may accelerate the pandemic.
“They’re a little late — everybody’s got their plane tickets,” said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center. “But better late than never.”
Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota and a member of Mr. Biden’s Covid-19 advisory board, warned that a Thanksgiving feast was the perfect setting for spreading the virus.
“This is a bad time to be swapping air with people that are not immediate household members,” he said. “You can have one person sitting at the table who appears to be perfectly healthy, and you can infect most the people, if not all of the people, sitting at that table.”
Small household gatherings help spread the virus, although their contribution to the overall toll has been hard to define. Older family members are particularly vulnerable to developing severe Covid-19, especially if they have chronic health conditions.
Traveling itself puts people at risk of exposure to the virus, regardless of how they travel. “What we’re concerned about is not only the actual mode of travel — whether it’s an airplane or bus or car — but also the transportation hubs,” Dr. Walke said.
“When people are in line to get on a bus or plane,” social distancing becomes difficult and viral transmission becomes more likely, he said.
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Even driving in a car poses risks, because travelers can be exposed at rest stops and gas stations. If Americans choose to travel, they must wash hands, wear masks and maintain social distancing, C.D.C. officials said.
Dr. Walke and others were at pains to differentiate between household members and family members. Many Americans believe that it is safe to gather with family, even if they don’t live together; in fact, most scientists say only other members of the household are safe company.
Researchers define a household as people who have been living together under the same roof for the last 14 days. That definition may apply to unrelated roommates who share living quarters but may exclude close family members who have been living apart from their parents.
The new recommendations pose a particular quandary for families anticipating the return of a college student or hoping to host an adult child who lives in a separate residence. Neither child is part of the household.
Colleges have encouraged students — many returning home for the remainder of the semester — to take a coronavirus test before they depart, but C.D.C. officials do not endorse testing before gathering for Thanksgiving.
Testing is far from foolproof, and a negative result indicates only that “you probably were not infected at the time your sample was collected,” according to the agency.
If members of different households are gathering in someone’s home for the Thanksgiving meal, they should all wear masks, except when eating, and remain six feet apart, federal officials said.
Guests should be encouraged to wash their hands with soap and water, and no one should hug or exchange handshakes. When gathering inside, attendees should wear masks as much as possible when not eating. Windows and doors should be kept open as much as possible to improve ventilation.
The C.D.C.’s advice went so far as to urge people to speak in low voices, because shouting — or singing — can spread the virus. Only one person should serve the food, federal officials said. If there are overnight guests, they should have their own bathroom.
Other medical organizations also issued dire warnings on Thursday. In an unusual “open letter to the American people,” groups representing physicians, nurses and hospitals jointly urged people to scale back holiday gatherings.
Though the letter did not explicitly discourage travel, the groups noted that Covid-19 cases had spiked after other holidays, like the Fourth of July and Labor Day, and that health care systems were already stretched to the limit in many parts of the country.
Michael Shear contributed reporting from Washington, and Karen Zraick, Shawn Hubler and Niraj Chokshi from New York. Jill Cowan contributed reporting from Los Angeles.
