WASHINGTON, Jan 7 (Reuters) - COVID-19 hospitalizations in the United States are poised to hit a new high as early as Friday, according to a Reuters tally, surpassing the record set in January of last year as the highly contagious Omicron variant fuels a surge in infections.

Hospitalizations have increased steadily since late December as Omicron quickly overtook Delta as the dominant coronavirus variant in the United States, although experts say Omicron will likely prove less deadly than prior iterations.

While potentially less severe, health officials have warned that the sheer number of infections caused by Omicron could strain hospital systems, some of which have already shown signs of distress, partly due to staffing shortages.

"I don't believe we've seen the peak yet here in the United States," Centers for Disease Control and Prevention (CDC) Director Rochelle Walensky told NBC News' "Today" program on Friday, as schools and businesses also struggle with rising caseloads.

The United States reported 662,000 new COVID-19 cases on Thursday, the fourth highest daily U.S. total coming just three days after a record of nearly 1 million cases was reported, according to the Reuters tally.

Newsletter signup for email alerts

The seven-day average for new cases set a record for a 10th consecutive day at 597,000, while COVID hospitalizations reached nearly 123,000 and appeared poised to top the record of over 132,000 set last year.

Deaths, an indicator that lags hospitalizations, remain fairly steady at a still high 1,400 a day, according to the tally, well below last year's record numbers.

Cautiously optimistic

New York Governor Kathy Hochul and the head of one of the largest U.S. hospitals both said they were cautiously optimistic that cases and hospitalizations would soon plateau in the state.

"We think with our modeling that the peak will happen next week," said Steven Corwin, chief executive of New York-Presbyterian Hospital, during Hochul's daily briefing.

Delaware, Illinois, Maryland, Pennsylvania, Ohio, Vermont and Washington, D.C., all reported record levels of hospitalized COVID patients in recent days, according to the Reuters analysis.

Hospitalization data, however, does not differentiate between people admitted for COVID-19 and so-called incidental positives. Those are patients who were admitted and treated for issues other than COVID-19 and contracted the virus while in the hospital and are counted in coronavirus hospitalization numbers.

Incidental infections have occurred throughout the pandemic but might be significantly higher now due to the staggering pace of Omicron's spread - a phenomenon that has prompted state health departments to consider altering their disclosures.

Starting next week, Massachusetts hospitals will report whether admissions are primary or incidental to COVID-19, said Kathleen Conti, a spokesperson for the state's department of health.

Rising cases have forced hospital systems in nearly half of U.S. states to postpone elective surgeries.

While many school systems have vowed to continue in-person instruction, some have faced ad hoc closures as cases rise. Chicago Public Schools, the third-largest U.S. school system, were closed for a third day on Friday amid a teacher walkout over COVID-19 protections.

U.S. and other officials have said schools can be safely opened, especially with widely available vaccines and boosters, and the CDC on Thursday issued new isolation policy guidelines for schools.

Officials continue to press vaccinations as the best protection against serious illness, although federal mandates requiring them have become politically contentious.

U.S. Supreme Court justices on Friday grilled Republican state officials and business groups seeking to block President Joe Biden's vaccine-or-testing mandate for large businesses and pressed the administration to justify the policy at a time of surging COVID-19 cases nationwide.

The U.S. Food and Drug Administration on Friday shortened the interval between the primary series of the Moderna COVID-19 vaccine and a booster dose from six months to five for people aged 18 or older.

The regulatory decision comes days after the agency made a similar move for getting a booster shot of the Pfizer and BioNTech COVID-19 vaccine. The Pfizer booster has also been authorized for use in children aged 12 to 15.

(Reporting by Susan Heavey, Lisa Shumaker, Maria Caspani, Ankur Banerjee, and Nathan Layne Editing by Jonathan Oatis and Bill Berkrot)