Nearly all of the sequenced cases in America are now omicron-based, which has led to a huge increase in infections that could disrupt everyday life and strain hospitals.

According to the Centers for Disease Control and Prevention data, Omicron was responsible for 95% of all sequenced Covid cases within the U.S. over the week that ended on New Year’s Day. The once-dominant Delta variant now accounts for only 4.6%.

The CDC routinely collects Covid virus samples and analyses their genetic sequences. This allows them to discover new variants, and which strains are circulating in America.

Delta has been overtaken by the contagious variant omicron in just a few weeks. Delta represented 91%, while omicron was represented in less than 1 percent of the sequenced cases as of December 1.

Johns Hopkins University’s data shows that the U.S. had a record-breaking pandemic of over 1 million infections. A CNBC analysis of Hopkins data shows that the United States is reporting an average seven-day count of nearly 480,000 new infections.

Omicron causes a rise in Omicron cases at least partially because it can partly evade immunity from vaccines, and is capable of causing breakthrough infections in large numbers.

Joe Biden, the President, stated Tuesday that those who are completely vaccinated (especially boosters) are extremely protected against serious illness from Omicron even though they may be infected.

Covid can be obtained, however, it’s extremely unlikely you’ll get seriously ill from it. Biden said about people who are vaccinated. “We are witnessing Covid-19 cases at vaccinated offices across America including the White House. But, if you’ve been vaccinated, you are very protected.”

study published by the U.K. Health Security AgencyThis was the conclusion of last week PfizerAnd Moderna’sA two-dose shot is only around 10% effective for preventing symptomatic infection due to omicron twenty weeks following the first dose. According to this study, however, the two-dose vaccines provide protection against serious illness.

The U.K. Health Security Agency determined that booster doses offer the greatest protection and up to 75% effectiveness in the prevention of symptomatic infections. Because the U.K. was where the outbreak of the Omicron Wave began, U.S. health officials have closely monitored data from the U.K.

Biden warned that people not vaccinated against omicron spreading quickly in the U.S. and warned many will be infected.

“Some will die — needlessly die,” Biden said. The unvaccinated take up hospitals beds, crowding emergency rooms, and intens care units. This has displaced others who are in need of those hospitals.”

Public health officers and scientists are trying to figure out the extent of the illness that omicron can cause compared to delta. In a study by the U.K. Health Security Agency it found that people who have been infected by omicron were less likely to be admitted for treatment than those who had delta.

study from the University of Hong Kong’s Faculty of MedicineOmicron lung infection is much less common than its original strain, suggesting that it may cause less serious disease. The study revealed that omicron reproduces in the human airways much more quickly than it does in animals, possibly explaining why it spreads so fast.

Susan Hopkins (UK Health Security agency chief medical advisor) cautioned it’s too early to determine the severity of the virus, since the variant has just begun to spread to more vulnerable people, including the elderly. Omicron should not be treated as mild because infected people are generally younger and have more positive clinical outcomes.

Hospitalizations in the United States are on the rise. According to data from the Department of Health and Human Services, approximately 98,000 Americans have been hospitalized using Covid-19 as of January 3, an increase of 32% over a week.

small study out of South AfricaIn November 2011, the first public alert about omicron was issued. It found that individuals infected by this variant of omicron may be more immune to it than others. According to the study, this could lead to omicron displace delta in co-circulating countries.

South Africa scientist team noted that the omicron could displace delta, and be milder. This would reduce Covid-19 severity and make it less disruptive to society.

Nate Rattner from CNBC contributed to this article.