The coronavirus appears set to dampen the festivities this holiday season for a second year in a row, as its new variant Omicron spreads around the world, threatening hospital workers already gasping for respite from the surging Delta cases.

Omicron accounted for about 3 percent of the COVID-19 cases sequenced nationally while the New York/New Jersey area of the country has the highest rate of 13 percent, director Rochelle Walensky of the United States Centers for Disease Control and Prevention (CDC) said on the CBS Mornings Tuesday.

Harvard experts evaluated these numbers to be underestimates as Omicron moves faster than the surveillance attempts.

"Our Delta surge is ongoing and, in fact, accelerating. And on top of that, we're going to add an Omicron surge," an infectious diseases expert Dr. Jacob Lemieux told the AP. He monitors variants for a research collaboration led by Harvard Medical School.

"That's alarming, because our hospitals are already filling up. Staff are fatigued," he said.

Christmas plans hang in balance

Outside the U.S., Canada is facing similar struggles of medical resource exhaustion and the Canadian government has implored residents to avoid international trips ahead of holiday seasons as the spread of the Omicron accelerates.  

The president of European Union said on Wednesday that Omicron would become the dominant variant by mid-January, and declared that "once again, this Christmas will be overshadowed by the pandemic."

The UK on Wednesday recorded the highest number of confirmed new COVID-19 infections since the pandemic began, and England's chief medical officer warned that the situation is likely to get worse as Omicron drives a new wave of illness during the holidays. The country also reported its first death from Omicron on Monday.

Are the vaccines effective enough?

Earlier this week, a UK study found that the two-dose COVID-19 vaccine regimens from Oxford-AstraZeneca and Pfizer-BioNTech do not induce enough neutralizing antibodies against the coronavirus variant Omicron.

However, U.S. top infectious diseases expert Dr. Anthony Fauci said Wednesday that there is no need, for now, for an Omicron-specific booster shot. He said that the two-dose mRNA vaccines, the Pfizer and Moderna shots, still appear to offer considerable protection against hospitalization from Omicron.

At the same time, the U.S. White House on Wednesday insisted there was no need for a lockdown because vaccines are widely available and appear to offer protection against the worst consequences of the virus.

In many ways, Omicron remains a mystery. It was first reported from South Africa, indicating it may cause milder symptoms compared with Delta but be better at evading vaccines.

Globally, more than 75 countries have reported confirmed cases of Omicron, while 36 states in the United States have detected the variant.