Millions of Americans carried on warily with travel plans through a second pandemic-clouded holiday season, despite a growing wave of COVID-19 infections driven by the Omicron variant, though many were forced to scale back their ambitions.

COVID-19 infections have surged in the United States in recent days due to Omicron, which was first detected in November and now accounts for nearly three-fourths of U.S. cases and as many as 90% in some areas, such as the Eastern seaboard.

The average number of new COVID infections has risen 37% to 165,000 per day over the past week, according to a Reuters tally.

Daily totals of deaths and hospitalizations, considered lagging indicators, were little changed nationwide over the past seven days, but have jumped 55% and 28%, respectively, over the course of December.

At least six states - Illinois, Maryland, Massachusetts, New Jersey, New York and Ohio - all set one-day records for new cases this week, according to the Reuters tally.

Anticipating an even larger flood in cases requiring medical attention, the Centers for Disease Control late Thursday cut its recommended quarantine period for COVID-positive healthcare workers who are asymptomatic to seven days from 10.

While Americans scrambled for COVID-19 tests and weighed varying public health guidance about how to gather safely, many were determined to brave the latest surge to enjoy some semblance of holiday celebrations and tradition.

The Transportation Security Administration on Wednesday screened 2,081,297 passengers through the nation's airports, an increase of 144,000 over the number of travelers it screened pre-pandemic on the same date in 2019.

In-person Christmas services will be held at all churches and parishes in the Roman Catholic Archdiocese of New York, which includes more than 2.5 million worshipers across 10 counties, spokesperson Joseph Zwilling said.

Although Omicron has prompted no new restrictions, the Archdiocese will maintain mask-wearing and social distancing rules it first instituted last year.

"The existing measures have been working," Zwilling said.

U.S. health officials have said people who are fully vaccinated should feel comfortable proceeding with holiday travel and family gatherings. They warned those who are unvaccinated are at higher risk of getting seriously ill or dying from the virus.

Omicron's rapid spread will also put a damper on New York's iconic New Year's Eve celebration for a second straight year. Mayor Bill de Blasio said attendance for the midnight ball drop in Times Square will be capped at 15,000, roughly a quarter of the typical pre-pandemic crowd size.