• New U.S. Covid cases are at a record seven-day average of more than 265,000 per day as of Tuesday, surpassing the previous high mark of about 252,000 average daily cases set on Jan. 11, 2021.
• The new pandemic peak comes as the delta and omicron variants are circulating simultaneously across the country.
• About 75,000 Americans are hospitalized with Covid-19 and the country is reporting more than 1,500 daily deaths. Though both figures are rising, they are lower than when the last daily case record was set nearly a year ago.

U.S. Covid cases have hit their highest level of the pandemic as two highly infectious variants circulate throughout the country and health officials urge Americans to get vaccinated and boosted against the virus.

Nationwide daily new cases were at a record seven-day average of more than 265,000 as of Tuesday, according to data compiled by Johns Hopkins University, surpassing the previous high mark of about 252,000 average daily cases set on Jan. 11, 2021.

The fresh pandemic peak comes as the delta and omicron variants are spreading simultaneously. The previously dominant delta variant was already driving U.S. case counts higher this fall before the emergence of omicron, which is contributing to a near-vertical rise in daily new cases. 

About 75,000 Americans are hospitalized with Covid-19 and the country is reporting more than 1,500 daily deaths. Though both figures are rising, they are lower than when the last daily case record was set nearly a year ago, before Covid vaccinations were widely available. Hospitalizations topped 137,000 at that point, according to a seven-day average of data from the Department of Health and Human Services, and Johns Hopkins data shows the average death toll was more than 3,200 per day.

Roughly 62% of the U.S. population is fully vaccinated with two doses of the Pfizer or Moderna shots or one dose of the Johnson & Johnson vaccine as of Tuesday, according to the Centers for Disease Control and Prevention. 

U.S. health officials have warned that the risk remains highest for the unvaccinated and are pushing Americans to get a booster dose to better protect themselves against omicron.

"It's got over 50 mutations, and because of those mutations just being vaccinated with two doses may not be enough," CDC Director Dr. Rochelle Walensky told CNBC's "The News with Shepard Smith" last week. "And so we really do need people to get boosted in order to increase their protection, especially against severe disease and death with omicron."

In the United States, omicron represented 59% of sequenced Covid cases while delta represented 41% last week, according to CDC estimates.

While the global scientific community is still gathering data on the new variant, which was first detected in southern Africa in late November, there has been some encouraging early news. Real-world studies from South Africa and the United Kingdom suggest that people infected with omicron develop more mild illness compared with delta, and Pfizer and Moderna have each said that a third dose of their mRNA Covid vaccines appears to provide significant protection against omicron, though a two-shot regimen has been found to be less effective against infection.

A more mild disease with greater transmissibility could still wreak havoc on health-care systems if the absolute number of cases gets high enough, experts say. That's because even if a smaller share of people infected end up going to the hospital, that smaller share of a very large number could be enough to strain hospitals and impact care for both Covid and non-Covid patients.

"A higher peak can further overwhelm the system for other people as well," said Dr. Bruce Y. Lee, a professor of health policy and management at the City University of New York School of Public Health, explaining that fuller hospitals would make it harder to treat those with heart attacks or cancer or who, for example, got into a car accident. 

The White House will deploy 1,000 military medical personnel to support hospitals facing a surge of patients infected with Covid this winter, President Joe Biden announced last week. The government will also purchase 500 million at-home tests that Americans can order online for free with delivery beginning in January.

Americans are struggling to get tested during the busy holiday season, when many are navigating crowded airports to visit family. There's a shortage of at-home test kits, with national and independent pharmacies struggling to keep them in stock. Lines to get tested onsite at clinics in cities such as New York are sometimes hourslong.

In an interview with ABC News that aired the day after the announcement, Biden said he wished he had ordered the test kits two months ago.

A number of states are reporting record daily new case count averages. New Jersey, Pennsylvania, New York, Rhode Island, Massachusetts, Virginia, Illinois, Maryland and Hawaii were each at all-time highs as of Tuesday, a CNBC analysis of Johns Hopkins data shows. Ohio was just shy of a record level, and Connecticut, Delaware and the District of Columbia all hit records in December before dipping back below their new peaks.

Hospitalizations are rising in nearly all of these states. The seven-day average of 325 patients in hospital beds with Covid in D.C. is a 70% increase from the prior week, nearing a record, while Hawaii, New Jersey, New York and Virginia have each seen weekly increases of 20% or more.

Anil Mangla, D.C.'s top epidemiologist, said that while the sources of outbreaks are similar to those throughout the pandemic – schools, restaurants and bars, event venues, and people's homes – the surge is much higher than expected. The district is reporting about 2,000 average new daily cases, according to Johns Hopkins data, roughly 10 times that of two weeks ago and more than any state on a population-adjusted basis.

"It's very obvious that omicron is here," Mangla said. "Is there delta? Absolutely. But because of the significant spike, we are definitely convinced omicron is here."

Mangla pointed to the decreasing percentage of D.C. Covid cases who were hospitalized, which is down to 2.6% from more than 5% earlier in the month, as a potentially hopeful sign that omicron causes milder disease. Infections in D.C. have only spiked in recent weeks, however.

Both delta and omicron are being detected in tests sequenced at Ohio State University, said Dr. Carlos Malvestutto, an infectious diseases physician at the university's Wexner Medical Center in Columbus. Though most of the patients currently in the hospital there are likely sick with delta, he said, omicron is now being seen in the majority of new Covid test results.

Most of the hospitalized patients are unvaccinated, according to Malvestutto, a trend that he expects to see with omicron as well. And even if the variant causes milder disease, he still thinks the state will surpass its pandemic high hospitalization level set in December 2020, when more than 5,600 patients were hospitalized with Covid. That figure is nearly 5,200 as of Tuesday.

"A lot of the data that we've been looking at tells us that even though the virulence appears to be significantly lower, because of very high transmissibility, in terms of absolute numbers it's likely to still lead to an increase in hospitalizations," he said. "If you are vaccinated and boosted, then you are in much better shape."

 — CNBC's Spencer Kimball contributed reporting.