Lifestyle Health COVID Variant Omicron Now Accounts for More Than 70 Percent of U.S. Cases, CDC Says Omicron makes up an even larger portion of COVID-19 cases in parts of the country including the New York region and the Pacific Northwest, where it accounted for more than 90 percent of cases last week By Katie Campione Katie Campione Digital News Writer, PEOPLE People Editorial Guidelines Published on December 20, 2021 08:14 PM Share Tweet Pin Email The new COVID-19 variant omicron accounted for a majority of reported cases in the United States last week. According to data published by the Centers for Disease Control and Prevention, 73.2 percent of coronavirus cases reported between Dec. 12 to Dec. 18 were omicron. Another 26.6 percent of cases were the delta variant. This represents a significant increase in the spread of omicron across the country. The week prior, omicron accounted for just 12 percent of cases in the U.S., the CDC reported. Omicron makes up an even larger portion of COVID-19 cases in parts of the country including the New York region and the Pacific Northwest, where omicron accounted for more than 90 percent of cases last week. Health officials have been scrambling to learn more about the new variant since it was first spotted in South Africa. The strain is the most contagious yet, has more mutations than any before it and seems to evade the previously-effective two-dose vaccines from Pfizer and Moderna. However, new studies suggest that receiving a booster shot can have an increased effectiveness in fighting off the rapidly spreading variant. Vaccine. Getty Omicron Is Moving Fast — but a Booster Shot Offers Significant Protection from Infection Researchers tested the variant against the antibodies of people who received the various COVID-19 vaccines and found that they all are less effective with omicron than earlier variants like delta. Johnson & Johnson and AstraZeneca, in particular, made no difference against omicron. But in people who had received a booster shot, they had enough antibodies to fight off omicron from creating an infection. One study from the U.K. found that while omicron reduces the two-dose vaccine series from Pfizer to just 34 percent effectiveness in preventing infection, getting a booster dose brings that protection back up to 75 percent. Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories. And though the vaccines are less effective in preventing infection with omicron, they are still extremely protective against severe illness that could lead to hospitalization or death. Cases of omicron in vaccinated people have been mild or asymptomatic, with patients recovering within three days, according to a large study from South Africa. After an incubation period of three to four days, patients first reported experiencing a scratchy throat, which then transitioned into nasal congestion, a dry cough and muscle aches and pains. Last month, the CDC expanded its vaccine booster recommendations for Americans following the arrival of the Omicron variant in North America. The spread of the variant "further emphasizes the importance of vaccination, boosters, and prevention efforts needed to protect against COVID-19," the CDC said. "Early data from South Africa suggest increased transmissibility of the Omicron variant, and scientists in the United States and around the world are urgently examining vaccine effectiveness related to this variant." As information about the coronavirus pandemic rapidly changes, PEOPLE is committed to providing the most recent data in our coverage. Some of the information in this story may have changed after publication. For the latest on COVID-19, readers are encouraged to use online resources from the CDC, WHO and local public health departments. PEOPLE has partnered with GoFundMe to raise money for the COVID-19 Relief Fund, a GoFundMe.org fundraiser to support everything from frontline responders to families in need, as well as organizations helping communities. For more information or to donate, click here.