The COVID-19 Omicron Variant

Medically Reviewed by Dan Brennan, MD on January 03, 2023

In November 2021, the World Health Organization (WHO) first identified the Omicron mutation of the COVID-19 virus as a variant of concern. It quickly became the most common strain worldwide.

Since then, several sub-variants of Omicron surfaced, including BA.2, BA.3, BA.4, and BA.5. By the summer of 2022, the BA.5 variant was the most dominant strain in the US. It and the BA.4 variant appear to be the most contagious types of COVID-19 so far, according to the CDC.

Omicron variants seem to cause less serious illness than earlier types of this coronavirus. The COVID-19 vaccines still work well to protect people against hospitalization and death and the new bivalent vaccine targets both the original strain as well as Omicron.

What Are the Symptoms of Omicron?

Early studies found that cold-like symptoms were common in those with Omicron. They reported that the top five symptoms related to the variant were:

But other common COVID-19 symptoms, like cough, fever, and loss of smell or taste, are still important signs to watch out for with the Omicron variant.

WHO experts have said there isn’t any data that suggests Omicron causes symptoms that are different from the ones produced by other COVID-19 variants.

How Severe Is Omicron?

Omicron typically causes less severe disease than other variants. However, some people may still get very sick, need to be hospitalized, and could die from an Omicron infection.

Having a less severe case of COVID-19 is especially true for instances of reinfection or breakthrough cases in people who are fully vaccinated. One early study has found that a previous infection only gives a 19% protection rate. It puts the chances of getting re-infected at almost 5½ times higher with this variant than with the Delta variant.

Remember that even a relatively mild case of COVID-19 can cause long COVID: symptoms that last for weeks or months after the first illness has passed.

How Quickly Does Omicron Spread?

Omicron spreads more easily than earlier variants of COVID-19, including Delta.

Studies suggest the incubation period for Omicron is a median of 3 to 4 days.

What Do We Know About Omicron Subvariants?

Omicron BA.2 or "stealth" subvariant. Scientists named this variant Omicron BA.2 to distinguish it from the original Omicron variant, BA.1. At first, scientists thought BA.2 wasn’t as contagious as BA.1 and would fade away soon. That didn’t happen. Starting in January 2022, BA.2 appeared to be at least as easy to transmit as BA.1.

A January 2022 study in Denmark showed no difference in the number of hospitalizations caused by BA.2 compared to BA.1. It also showed that as BA.2 cases went up, BA.1 cases went down. But other countries (Great Britain, Norway, and Sweden) reported slower BA.2 increases.

Early studies showed that current vaccines and boosters seemed to work at least as well against this variant, protecting against a first infection as well as against serious illness if you do get infected.

BA.4 subvariant. Experts first detected the BA.4 subvariant in South Africa in early 2022, followed shortly by the BA.5 subvariant. Since then, the numbers of countries and cases linked to these variants have spiked.

Both BA.4 and BA.5 have mutations that make them different from previous Omicron subvariants. These mutations affect the "spike" proteins that help the virus latch onto and infect your cells.  This makes infection easier. It also helps BA.4 and BA.5 elude virus-fighting antibodies from previous infections with COVID-19.  

BA.5 subvariant. One main difference is that BA.5 seems to spread more easily than BA.4. In late July 2022, BA.5 was responsible for about 78% of COVID cases in the U.S., compared to 13% for BA.4. Along with the spike protein mutation, BA.5 has additional mutations that distinguish it from BA.4.

Experts believe that symptoms of BA.4 and BA.5 are similar to those past variants. They include:

  • Constant cough
  • Fatigue
  • Sore throat
  • Runny nose
  • Headache

How Do Doctors Diagnose Omicron?

To find out if you have the virus, you’ll need to take a COVID-19 test. You can access at-home tests or see a doctor to get one. If you test positive, more testing would be needed to tell if your case was caused by the Omicron variant. But this process takes a long time and is expensive. Experts don’t usually do it for each positive COVID-19 case. The tests are also done anonymously to protect people’s privacy, so you won’t get that information.

How Do Doctors Treat Omicron?

Researchers continue to look at how well current COVID-19 treatments help with Omicron cases. Because of the genetic changes in the Omicron variant, some treatments will continue to be effective while others may be less useful. Your doctor may suggest antiviral medicines or monoclonal antibody treatments as an outpatient depending on your risk factors for serious disease from COVID-19.

Corticosteroids and IL6 receptor blockers still help people with severe COVID-19 infections.

Does the COVID-19 Vaccine Protect Against Omicron?

The BA.4 and BA.5 variants are close enough to the original Omicron virus that existing COVID-19 vaccines help prevent serious illness. So it's important to get your COVID-19 vaccine and boosters.

The new bivalent booster vaccine targets both the original strain as well as Omicron.

How Can You Prevent Omicron?

There are many things you can do to protect yourself from Omicron and other COVID-19 variants:

Get vaccinated. Vaccines are still the best public health step to protect people from serious illness from COVID-19. Get boosters if you're eligible.

Wear a high-quality mask. Your mask will protect you and those around you from all variants. The CDC suggests that you wear a mask in public indoor areas, regardless of whether you’ve had the COVID-19 vaccine, if the COVID-19 community level is high or if you prefer to be masked.  Also wear a mask if you or a family member are at high risk for severe COVID-19 disease even if the community level is at medium.

Social distance. It’s important to continue to social distance to stop the spread of Omicron when there is a threat of COVID-19 in the area.

Get a test. Self-tests or tests given by medical professionals can tell you if you have COVID-19 or not. These tools can help you take steps to protect others from Omicron and other variants.

Other safety measures. Open your windows to improve ventilation, keep your hands clean, stay away from crowded or poorly ventilated areas, and cough or sneeze into your elbow or a tissue.

Show Sources


BMJ: “Covid-19: Runny nose, headache, and fatigue are commonest symptoms of omicron, early data show.”

CDC: “About Variants,” “Variant Proportions,” “Unpacking Variants,” “Use and Care of Masks,” “Omicron Variant: What You Need to Know,” "COVID Data Tracker Weekly Review."

Eurosurveillance: “Outbreak caused by the SARS-CoV-2 Omicron variant in Norway, November to December 2021,” “Shorter serial intervals in SARS-CoV-2 cases with Omicron BA.1 variant compared with Delta variant, the Netherlands, 13 to 26 December 2021.”

GAVI: “Five things we’ve learned about the BA.4 and BA.5 Omicron variants.” “A second version of omicron is spreading. Here's why scientists are on alert.”

Statens Serum Institut: “Now, an Omicron variant, BA.2, accounts for almost half of all Danish Omicron-cases.”

UK Health Security Agency: “COVID-19 vaccine surveillance report Week 4.”

University Hospitals Cleveland: “Long-Haul COVID-19: Lingering Health Problems Even With Mild Symptoms.”

University of Minnesota Center for Infectious Disease Research and Policy: “Uncertainty swirls around Omicron COVID-19 severity.”

World Health Organization: “Update on Omicron.”

National Institutes of Health: “Interleukin-6 Inhibitors.”

Johns Hopkins Bloomberg School of Public Health: “An Update on Omicron Subvariants.”

Nature: “What Omicron’s BA.4 and BA.5 variants mean for the pandemic.”

MD Anderson Cancer Center: “COVID-19’s BA.4 and BA.5 Omicron subvariants: 12 questions, answered.”

UC Davis Health: “Omicron BA.5: What we know about this COVID-19 strain.”

Rochester Regional Health: “What We Know about the BA.5 Omicron Variant.”

© 2023 WebMD, LLC. All rights reserved. View privacy policy and trust info