Since identifying the first case of the Omicron variant in the United States on December 1, 2021, CDC has been working with state, tribal, local, and territorial public health officials to monitor the spread of Omicron in the United States. On December 10, 2021, CDC released an MMWR article summarizing characteristics of the first Omicron infections in the country.

CDC has also identified a rapid increase in infections consistent with what has been observed in other countries. Increases in infections are most likely due to a combination of two factors: increased transmissibility and immune evasion (the ability of the variant to evade immunity conferred by past infection or vaccination). Though the precise contribution of each of the two factors remains unknown, a substantial degree of immune evasion is likely as has been demonstrated in early in vitro studies.

CDC uses genomic surveillance to track variants of SARS-CoV-2 in the United States. CDC’s national genomic surveillance can detect a variant that is circulating at 0.1% frequency with 99% statistical confidence. Current-week estimates of variant proportions are provided by CDC’s Nowcast modeling data, enabling timely public health action while specimens are undergoing the two- to three-week sequencing and analysis process.

As of the week ending December 25, 2021, Nowcast estimated that Omicron accounted for 95.4% of circulating SARS-CoV-2 strains while Delta accounted for 4.6% of circulating strains.

The clinical severity profile of Omicron infection will strongly influence its impact on U.S. hospitalizations and deaths. A study from South Africaexternal icon demonstrates that in the first four weeks of the Omicron variant wave there were lower rates of hospitalization compared to the first four weeks of the Beta- or Delta-dominated waves in Gauteng Province. There was also less severe illness reported for those that were admitted. A study conducted in Canadaexternal icon found that the risk of hospitalization was 54% lower for Omicron cases compared with Delta cases.

Even if the proportion of infections associated with severe outcomes is lower than with previous variants, the absolute numbers of people with severe outcomes could be substantial given the rapid increase in the number of infections over the past three weeks. In addition, demand for ambulatory care and supportive care for treatment of mild cases could also stress the healthcare system.

Geographical differences in the predominance of the Omicron variant versus ongoing Delta variant infections and the rising burden of illness caused by other respiratory pathogens, such as influenza, may stress healthcare systems regionally to various degrees. On December 23, 2021, CDC issued updated guidance to enhance protection for healthcare personnel, patients, and visitors to address concerns about potential impacts on the healthcare system given a surge of SARS-CoV-2 infections. On January 4, 2022, CDC also issued updated guidance on quarantine and isolation for the public.

Some studies have demonstrated the importance of booster doses in protecting against infection with Omicron, and a lower effectiveness of the primary series of vaccines alone. Current CDC recommendations for vaccines and booster shots are expected to protect against severe illness, hospitalizations, and deaths from infection with the Omicron variant. Therapeutics, including monoclonal antibody treatments and antivirals, are also available for preventing and treating COVID-19 in specific at-risk populations.

These therapeutics differ in efficacy, route of administration, risk profile, and whether they are authorized by the U.S Food and Drug Administrationexternal icon for adults only or adults and certain pediatric populations. Some therapeutics are in relatively short supply, but availability is expected to increase in the coming months. Current recommendations were summarized in a CDC Health Alert Network Health Advisory, Using Therapeutics to Prevent and Treat COVID-19, published December 31, 2021.

Scientists around the world, including researchers at CDC, are working quickly to learn more about the Omicron variant. The recent emergence of Omicron and the fact that Delta is still a circulating variant further emphasize the importance of getting a primary vaccination series and, if eligible, a booster and continuing prevention measures.

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Original links to the article: - https://www.cdc.gov/coronavirus/2019-ncov/covid-data/covidview/index.html