The federal health officials shortened the isolation period for many Americans with coronaviruses on Monday in order to minimize disruptions to the economy and everyday life.
The cancellation of thousands of flights due to staff shortages has upended holiday travel, and now threatens industries as diverse as health care, restaurants and retail. The country is in the early stages of a surge.
The director of the Centers for Disease Control and Prevention said that the Omicron variant has the potential to impact all aspects of the society.
The agency had previously recommended that patients be isolated for 10 days after being tested for the virus. The period was cut to five days for those without symptoms or those with other symptoms.
After their isolation periods are over, Americans should wear masks around other people.
The updated guidance comes amid a rising tide of infections that threatens to swamp the U.S. health care system. Dr. Walensky said the new recommendations balance what we know about the spread of the virus and the protection provided by vaccination and booster doses. People can continue their lives with these updates.
The C.D.C. did not recommend that Americans take rapid tests before they are released from isolation.
The health officials shortened the period for Americans who were exposed to the virus. They said that people who were unvaccinated had to stay out of the public eye for five days. It also applied to people who had not received a booster shot for their Johnson & Johnson vaccine, or who had not received a Moderna vaccine.
The officials said that Americans who had received booster shots did not need to be in a hospital. People who have been exposed are encouraged to wear masks for 10 days and get tested five days after being exposed.
The C.D.C. reduced the number of days it recommended that health care workers who test positive should be isolated.
The Omicron variant has moved quickly across the country, from New York to Hawaii, where there have been more coronaviruses cases in the past week than in any other seven-day period. Delaware, Massachusetts, New Jersey and Puerto Rico have all reported record caseloads.
Over the past 14 days, the national average of new daily cases has increased by 83 percent. The seven-day average of deaths increased by 3 percent during that time.
Hospitalizations are up, but not as much as cases. More than 71,000 Americans are hospitalized with Covid-19, 8 percent higher than two weeks ago, but still below previous peaks.
In New York, Mayor Bill de Blasio implemented a vaccine mandate for private businesses. Employers in New York City have to verify that their workers have received a vaccine.
Travelers arriving on domestic flights in Puerto Rico are required to show a negative Covid test if they want to avoid a fine. 300 National Guard members were sent to hospitals and ambulance service providers in Massachusetts on Monday.
President Biden spoke of cooperation at various levels of government during a conference call with governors on Monday. Asa Hutchinson, the Republican governor of Arkansas, praised the president's plan to give away 500 million rapid at- home tests, but said that federal efforts to stanch the infections must yield to state remedies.
There is no federal solution, Mr. Biden said. This is solved at the state level.
The patient is in need of help or preventing the need for help when the rubber meets the road.
Some business owners said the new C.D.C. guidance was helpful in addressing staffing shortages. They said that it left employers and their workers with the challenge of determining how long people should be isolated from each other.
Barbara Sibley, who runs four restaurants in New York City and is currently isolating with Covid, said that the change doesn't really take the burden away.
The guidance could be used by companies to rush employees back to work, making it harder for workers to get paid sick leave. Sara Nelson, the president of the flight attendants union, said that they can't allow fatigue to lead to decisions that extend the life of the Pandemic.
Some scientists said that it was time to shorten the isolation periods for people who have been exposed to the Pandemic.
The dean of the Brown University School of Public Health said that people who tested positive for an infectious disease would usually be out of it by a few days.
He said that the personal and social costs of 10-day isolation periods were considerable because of the difficulties faced by single parents. He was worried that some people, especially those who rely on hourly wages, were not getting tested because of the toll of missing work.
Dr. Jha said that it was hugely harmful to ask people to be isolated. If you can shorten that isolation in a way that is clinically responsible, I think it will lower the bar for people to get tested.
The C.D.C. should have recommended a negative rapid test before people ended their isolation, said Dr. Jha. This is a reasonable approach given that tests are not widely available.
The C.D.C.'s new guidance was called reckless by Dr. Michael Mina, an expert on rapid tests. There were different periods during which people remained contagious.
Other scientists said that some people may be catching their infections in the very early stages with more people testing regularly. Five days may not be enough to stop people from spreading the virus.
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Joseph Fauver is a genomic epidemiologist at the University of Nebraska Medical Center. I was surprised that they did not have a testing requirement for it or a vaccine status requirement.
Dr. Fauver co-authored a study on the duration of infections with an earlier variant in N.B.A. personnel. He said that the change of tack from the C.D.C. had not been supported by data.
Vaccination is a good way to protect against illness. According to the C.D.C., unvaccinated people are five times more likely to test positive and 14 times more likely to die of Covid than vaccine patients.
The nation's medical infrastructure is dangerously damaged two years into the Pandemic as hospitals contend with staff shortages fueled by burnout and early retirements.
Public health experts said that the most severe disruptions could still happen.
The past surge of the coronaviruses has allowed states to reallocate resources, while this wave threatens to overtake the country at once, said Michael Osterholm, a professor and director of the Center for Infectious Disease Research and Policy at the University of Minnesota.
All 50 states are in the same place at the same time. He said it was like every state was being hit by a storm.
In the next three to five weeks, a lot of health care workers will get infections and be unable to work, straining the overburdened system. He said that they were already stretched so thin.
Scientists said that the staffing shortages in hospitals and nursing homes had increased the need for re-evaluating isolation periods. People were able to get a rough, if imperfect, measure of whether they were infectious with the help of at- home rapid tests.
Scientists said that the scarcity of those tests over the holiday period made it more difficult to recommend isolation. Dr. Jha said that two negative rapid tests on consecutive days would offer more reassurance that someone was not contagious.
Changing isolation policies were more difficult because of a lack of widespread access to tests.
The federal health officials are trying to prepare for a crisis, so it is difficult, according to a Louisiana State University Health Sciences Center Shreveport researcher. There are many unknowns.
Data from South Africa and some European countries show that Omicron infections are milder. Experts warn that might not be true.
Akiko Iwasaki, an immunologist and researcher at the Yale School of Medicine, said that they cannot assume the same things will happen in the U.S. We still need to make sure that the people who are unvaccinated are protected.
Bill Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health, cautioned that it was not certain how well rapid tests would measure contagiousness with Omicron.
He said that people who have been vaccined can only shed the Omicron variant in large amounts. The variant could quickly shut down a workplace.
Albert Sun, Emma Goldberg, Giulia Heyward, Joseph Goldstein, Michael D. Shear, Sabrina Imbler, and Lauren Hirsch contributed to the report.
