Coronavirus updates: US reports nearly 300,000 new cases in all-time high

The U.S. Centers for Disease Control sent out a statement following the first discovery of the UK variant of the coronavirus in Colorado.

"We expect that there will be additional cases that are likely to be detected in the coming days," the agency said in its statement.

"Viruses constantly change through mutation, and new variants of a virus are expected to occur over time. Multiple variants of the virus that causes COVID-19 have been documented in the United States and globally during this pandemic."

The CDC added that the UK variant doesn't appear to cause more severe disease or mortality, but warned it does appear to have a higher transmission rate.

"Based on studies with other viruses containing similar mutations, CDC believes there will be little or no impact on immunity from natural infection or vaccination," the agency said.

-ABC News' Anne Flaherty contributed to this report.

A man in his 20s in Colorado is confirmed to have the COVID-19 variant that was detected in the United Kingdom, Colorado officials said.

This is believed to be the first known case of the variant in the U.S.

The man, who’s had no travel history, is in isolation, officials said.

“Public health officials are doing a thorough investigation,” Colorado officials said. “The individual has no close contacts identified so far, but public health officials are working to identify other potential cases and contacts through thorough contact tracing interviews.”

The variants are all the same virus, no matter their small genetic differences. SARS-COV-2 is a respiratory virus, meaning it is transmitted through droplets, so masks and social distancing still work to slow transmission, no matter the variant.

Colorado Gov. Jared Polis reiterated that health officials will monitor the case closely.

"We are working to prevent the spread and contain the virus at all levels," he said in a statement.

Stay-at-home orders are extended in California’s hard-hit Southern California and the state's San Joaquin region, where ICU capacities remain at 0%.

Hospitalizations in the Golden State have increased 36.5% over the last two weeks; now 20,390 coronavirus patients are in hospitals.

ICU hospitalizations have increased 35.1% over last two weeks and now stand at 4,308 patients. 

Dr. Mark Ghaly, Secretary of California Health and Human Services, on Tuesday outlined plans for hospitals’ “crisis care” mode, which is when care for patients would have to be rationed. California is not there yet, he said, adding that it’s important to prepare.

"We certainly know SoCal hospitals are in crisis,” Ghaly said.

“Some hospitals in SoCal have put in place some practices that would be part of crisis care, whether it’s decisions about how ambulances are received or how stretched staff become,” Ghaly said. “But we have not heard of a hospital needing to make a decision between two patients who need ventilators and needed to make a decision between them or any care decisions like that.”

ICU capacity in California’s three other regions stand at: 10.4% in the Bay Area, 19.1% in Greater Sacramento and 27.9% in Northern California. All regions but Northern California are under stay-at-home orders.

ABC News’ Alyssa Pone, Alex Stone and Michelle Mendez contributed to this report.

Margaret Keenan, the 91-year-old grandmother in the United Kingdom who was the first in the world (outside of clinical trials) to get the Pfizer vaccine, got her second dose on Tuesday.

Keenan, then 90, received her first dose on Dec. 8.

ABC News’ Rashid Haddou contributed to this report.