Nations Shorten Recommended Quarantine Times for Covid-19 Patients

Her move comes after some airlines canceled dozens of flights due to staffing problems and some business leaders expressed concerns that government quarantine rules could cripple crucial operations unless updated.

Under New York’s new rules, critical workers seeking to return to work five days after a confirmed case must be fully vaccinated and either they don’t have symptoms or their symptoms are resolving and they haven’t had a fever for 72 hours.

Those returning will need to remain masked, Ms. Hochul said. “We need you again, we need you to be able to go to work,” Ms. Hochul added.

New York state’s move comes after the U.K. shortened its quarantine period to seven days for vaccinated people, and some airline executives wrote to the U.S. Centers for Disease Control and Prevention seeking an adjustment in agency isolation guidelines to avoid disruptions to operations.

On Thursday, the CDC revised its isolation and quarantine guidelines for healthcare workers, partly to help hospitals have enough staff to deal with any rise in admissions due to Omicron.

Under the new CDC guidelines, healthcare workers can go back to work within seven days following a negative test, or potentially even sooner in a staffing crunch. Also, healthcare workers who are fully vaccinated and who got a booster wouldn’t need to quarantine after high-risk exposure to the virus.

CDC said it may adjust its guidelines further as more information about Omicron emerges.

The changes suggest the march of the new strain, which has driven rapid and large increases in case counts around the U.S. and world, combined with the advent of new tools like booster shots is putting pressure on policy makers to calibrate pandemic-response measures.

Covid-19 is now on the path toward becoming endemic in the U.S., eventually dissipating into something like a regular seasonal illness, according to some public-health experts. The degree of disruption it causes will likely now depend on what level of disease—and restrictions—officials and individuals are willing to tolerate.

“It is a tug of war between society and the virus,” said Peter Chin-Hong, an infectious-disease specialist at the University of California, San Francisco.

In the U.S., the 7-day average of Covid-19 cases has eclipsed the peak during Delta’s march through the country. The average reached 182,682 as of Dec. 23, according to a Wall Street Journal analysis of Johns Hopkins University data; the last time the figure was higher was Jan. 21.

The more than 261,000 cases reported on Dec. 23 excludes states—Indiana, North Carolina, Mississippi and Kentucky—that have already started holiday blackouts for data.

U.S. airlines, including United Airlines Holdings Inc. and Delta Air Lines Inc., blamed Covid-19 as they canceled scores of flights for Christmas Eve and Christmas.

At both airlines, the cancellations account for a relatively small share of planned flying. So far, United has canceled about 182 flights scheduled for Friday, about 9% of its planned schedule, and about 111 that were slated for Saturday, according to FlightAware, a flight-tracking site.

Delta cut about 163 flights for Friday, about 8% of its planned schedule, and another 140 planned for Saturday.

To deal with increasing demand for testing, Ohio’s National Guard is running a mass testing site in Cleveland, while Palm Beach County, Fla., is opening one on Sunday. Ms. Hochul said New York would open 13 more state-run testing sites beginning next week, including one in each borough of New York City.

Though 95% of New York residents aged 18 or older have had at least one vaccine dose, Ms. Hochul said Friday morning, the state had 44,431 new positive cases in the latest day of reporting.

She said the state will be “highly recommending” that counties and school districts adopt test-to-stay policies, which would keep more students in school when classes resume in January.

“We want healthy kids to stay in school,” she said, adding that there will be at least two million take-home tests available by the time schools start again.

Omicron was first identified in South Africa just last month. Indications are mounting that the disease caused by the variant is milder than previous strains such as Delta and progresses faster, though researchers say more study is needed to make a firm determination.

A U.K. study released Thursday found that people infected with Omicron are between 50% to 70% less likely to be hospitalized than those who caught earlier strains. The U.K. Health Security Agency study follows similar findings from studies in Scotland and South Africa that also pointed to a substantially lower risk of hospitalization with Omicron than with earlier variants.

In the U.K., the head of the Royal College of Nursing, Pat Cullen, told the British Broadcasting Corp. that the National Health Service is struggling with staff absences as Omicron spreads. The U.K. Health Security Agency’s chief has indicated that the British government might decide whether to introduce more restrictions in England by assessing the wider social impact of the infection, rather than the severity of the disease itself.

Prime Minister Boris Johnson has said his government won’t introduce further restrictions before Christmas, but it is possible more measures would be introduced next week. Scotland, Wales and Northern Ireland have already announced wider social restrictions after Christmas.

Elsewhere, Thailand detected its first domestic cluster of Omicron transmissions, in Kalasin province, north of Bangkok. Bangkok also canceled city-led New Year celebrations, including midnight prayers that are typically held by thousands of Buddhist monks. In New York City, Mayor Bill de Blasio said on Thursday that attendance at the annual New Year’s Eve celebration in Times Square will be limited to 15,000 compared with the typical 58,000.

Austria has joined other countries now considering a fourth vaccination, which will be offered to healthcare workers and other key employees if it is approved. Israel has already made plans to offer a fourth shot to people over 60 years old, while Germany is considering a similar course of action.

Also in Europe, the Spanish government this week reintroduced an outdoor mask mandate amid a surge in infections. The Italian government did likewise on Thursday, the same day the country reported its highest number of daily infections since the start of the pandemic.

Write to Melissa Korn at melissa.korn@wsj.com and James Hookway at james.hookway@wsj.com