Omicron now dominant strain in U.S. COVID-19 cases

December 23, 2021 | by Edward-Elmhurst Health
Categories: Healthy Driven Life

This blog was originally posted in 2021. Some information may be out of date. For the latest updates on vaccines, testing, screening, visitor policy and post-COVID support, visit

With the holidays fast approaching, hospitals are filling up across the country as COVID-19 cases are quickly rising. In addition to the ongoing delta surge, the highly transmissible omicron variant has fueled a wave of new infections.

Since it was first identified in South Africa in November 2021, omicron has been spreading rapidly around the world and across the U.S., faster than any previously known form of the coronavirus.

When December 2021 began, omicron accounted for less than 1% of COVID-19 cases in the U.S. In just a few weeks, omicron has overtaken delta as the dominant COVID strain in the U.S., accounting for 73% of new infections last week (ending Dec. 18), according to data from the Centers for Disease Control and Prevention (CDC).

The CDC is expecting a surge of COVID-19 cases in the coming weeks.

Scientists are still learning about omicron. It’s not clear yet whether omicron causes more or less severe illness. Preliminary evidence from South Africa suggests that the omicron variant may cause less severe disease. Data from real-world coronavirus cases in Britain also suggest that omicron appears to be less severe than the delta strain, and less likely to send people to the hospital. There is still more to learn.

More research is also needed to determine how well COVID-19 vaccines work against omicron. Immunocompromised and elderly people are at particular risk.

While breakthrough infections in people who are fully vaccinated are likely to occur, the best way to slow the emergence of variants like omicron is to get vaccinated. Preliminary research suggests that full vaccination, plus a booster shot, provides strong protection against infection with omicron.

“All of us have a date with omicron,” said Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, told the AP. “If you’re going to interact with society, if you’re going to have any type of life, omicron will be something you encounter, and the best way you can encounter this is to be fully vaccinated.”

In addition to producing antibodies, COVID-19 vaccines produce T cells, which learn to recognize viral infected cells and destroy them. Preliminary research suggests that these T cells still recognize the omicron variant.

Boosters help to create an even stronger wall of defense. Both Pfizer and Moderna announced that a booster shot significantly increases the level of antibodies against omicron. Researchers found the effectiveness against infection jumped from just 34% after two doses to 75% after a booster.

Only about a third of fully vaccinated American adults have received a booster to date.

Everyone age 16 and older can get a booster if it's been at least 6 months since you completed your two-dose primary vaccination series with Pfizer or Moderna, or if it's been at least 2 months since you completed your single-dose primary regimen with Janssen (J&J).

Although a booster provides extra protection, two doses of the mRNA vaccine should still protect against severe infection with omicron. By far, the most vulnerable people are those who have never been vaccinated. There are about 50 million eligible Americans who have not yet gotten vaccinated.

With omicron and delta variants spreading across the country, getting vaccinated or boosted is the best way to prevent severe illness, hospitalization and death from COVID-19.

As always, you can add additional layers of protection by handwashing, masking up indoors and social distancing. Learn how to celebrate with COVID-19 caution during the holidays.

Edward-Elmhurst has COVID-19 vaccine appointments available to ages 5 and older, including booster doses for ages 16 and up. It is easy to schedule a vaccine appointment. You do not need a MyChart account. Schedule your COVID-19 vaccine now.

The information in this article may change at any time due to the changing landscape of this pandemic. Read more about COVID-19.

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