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In late November 2021, reports emerged of a new variant of SARS-CoV-2, the virus that causes COVID-19.

Known as the Omicron (B.1.1.529) variant, it has spread worldwide and in the United States. The Centers for Disease Control and Prevention (CDC) has classified Omicron as a variant of concern. It has become the dominant variant of SARS-CoV-2 spreading in the United States.

Scientists are studying the Omicron variant to learn more about it, including how it differs from previous variants. Here’s what is known so far.

What Is the Omicron Variant?

Like previous variants — such as the highly contagious Delta (B.1.617.2) variant — Omicron has multiple mutations from the original or most recent SARS-CoV-2 virus. Mutations are genetic changes in the virus.

Viruses change and mutate over time, which causes variants. There have been many variants of SARS-CoV-2 since the first detection of the virus in late 2019.

According to the WHO, Omicron “has a large number of mutations, some of which are concerning.”

Omicron came from a different strain of SARS-CoV-2 than Delta, which was the dominant variant in the U.S. before Omicron.

“It’s not surprising that we’re seeing the emergence of another variant,” says Graham Snyder, MD, medical director, Infection Prevention and Hospital Epidemiology, UPMC. “A virus can survive only by copying itself inside the body, which it does billions of times. Sometimes, a copy of the virus has a mistake — a mutation. When one or more mutations makes the virus more successful, that new variant of the virus will spread.

“A new variant may be more successful because it changes how we get sick, is easier to pass person-to-person, or is not as well-controlled by our immune system or the therapies that we have, or a combination of these factors.”

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How Is Omicron Different than Other Variants?

According to data from collected samples, Omicron has more than 50 mutations. More than 30 of those mutations are to the spike protein on the surface of the coronavirus. The spike protein is the area of the coronavirus targeted by COVID-19 vaccines.

The number of spike protein mutations that Omicron has is higher than the number seen in other variants, like Delta.

Is Omicron Worse than Other Variants?

Omicron is a variant of concern. Criteria for a variant of concern include the potential that the variant is more transmissible, causes more severe disease, and/or is less vulnerable to existing vaccines and treatments.

Scientists are continuing to study the transmissibility and severity of Omicron, along with the effectiveness of current vaccines and treatments. Preliminary data indicate:

  • The emergence of Omicron happened quickly. This suggests the variant is easily transmitted. According to the WHO, Omicron appears to spread faster than Delta and other variants.
  • A December 2021 study by Discovery Health reported the risk of hospitalization is lower for Omicron than previous variants. This suggests Omicron may cause less severe illness, but more data will be needed to be sure. Also, it is possible that even if Omicron is less severe, its higher transmissibility rates could lead to more hospitalizations and deaths.
  • Early data reported that two doses of the Pfizer-BioNTech and Moderna vaccines showed less effectiveness in preventing infection against Omicron. However, the vaccines were still effective in preventing severe illness, hospitalization, and death, which is the main goal of the vaccines. Also, Pfizer and Moderna booster doses increase the effectiveness against infection.
  • The FDA paused the distribution of previously authorized monoclonal antibody treatments as they showed less effectiveness against Omicron. The monoclonal antibody Evusheld is still available as a preventive measure.
  • The WHO says preliminary evidence suggests a previous COVID-19 infection may be poor protection against infection with the Omicron variant. The Discovery Health study reported the risk of reinfection is higher with Omicron than previous variants.

Scientists will continue to study Omicron to better understand it and how it compares to previous variants.

“There is a lot we have yet to learn about Omicron, including who is most likely to get sick, what are the patterns of illness it causes, how effectively and rapidly it spreads, and how well-prepared we remain through vaccines and treatments like monoclonal antibodies,” Dr. Snyder says.

How Can I Prevent Getting the COVID-19 Variant?

The best way to protect yourself against the Omicron variant is by getting the COVID-19 vaccine. The vaccine has been effective against previous variants, especially in preventing severe illness and death.

Preliminary data show that the initial courses of vaccine — two doses of Pfizer and Moderna and one dose of Johnson & Johnson/Janssen (J&J) — offer less protection against infection with Omicron than with previous strains. However, Pfizer and Moderna have reported that getting a booster dose of their vaccines provides greater protection.

“Vaccination continues to be the safest and most effective way to protect yourself and your loved ones from COVID-19,” says Erin McCreary, PharmD, infectious diseases specialist, UPMC.

Americans ages 5 and older are eligible for the COVID-19 vaccine. Also, many Americans are eligible for additional or booster doses of the vaccine. For information on who is eligible for additional doses, visit our website.

The Centers for Disease Control and Prevention (CDC) recommends that all Americans who are eligible for a booster dose should get one. If you are eligible for the COVID-19 vaccine or a booster dose and would like to schedule an appointment with UPMC, visit

Scheduling an additional dose? Don’t forget to bring your COVID-19 vaccine card with you to your appointment.

“It’s very likely that the current vaccines will continue to offer protection against Omicron,” Dr. Snyder says. “Boosters are recommended for all adults and can ensure your immune system remains prepared.”

In addition to getting vaccinated, it is important to follow other COVID-19 prevention protocols. That includes wearing a facemask that covers your nose and mouth while in public in areas where COVID-19 spread is high. It’s especially important if you are not fully vaccinated or if you are at high risk for COVID-19 complications.

If you are showing symptoms of COVID-19, don’t go to work or school and get tested as soon as possible. A lab test is necessary to confirm a COVID-19 diagnosis.

“My plea to you during this holiday season is that everyone who is eligible for COVID-19 and a flu vaccine, make the choice to get one,” says Donald M. Yealy, MD, senior vice president, and chief medical officer, UPMC. “That, plus masking when you’re indoors or in crowds with those who are not in your immediate family, are the best protection from COVID-19 and flu. If you get sick, stay home and get tested. That allows us to help you better.”

An early COVID-19 diagnosis also can help treatment begin more quickly. Monoclonal antibody treatment for COVID-19 is an effective treatment for COVID-19 if treatment begins within seven days of symptoms appearing.

Paxlovid™, an oral antiviral medication, also is available for the treatment of mild to moderate COVID-19. You can get it at a retail pharmacy with a prescription. COVID-19 patients should receive either Paxlovid or monoclonal antibodies — not both.

Patients must have a doctor referral and a high-risk medical condition to receive monoclonal antibodies at this time. Ask your doctor if you are a candidate. If you don’t qualify for monoclonal antibodies, ask your doctor if you qualify for Paxlovid.

UPMC remains committed to protecting our communities against COVID-19. For more information, visit our website.

Editor's Note: This article was originally published on , and was last reviewed on .

CBS News, Omicron: What We Know — and Don't Know — About the New COVID-19 Variant. Link

Centers for Disease Control and Prevention, CDC Statement on B.1.1.529 (Omicron Variant). Link

Centers for Disease Control and Prevention, CDC Expands COVID-19 Booster Recommendations. Link

New York Times, Omicron: What Is Known — and Still Unknown. Link

World Health Organization, Classification of Omicron (B.1.1.529): SARS-CoV-2 Variant of Concern. Link

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