The COVID-19 Omicron Variant

Medically Reviewed by Zilpah Sheikh, MD on August 17, 2023
9 min read

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.

photo of man using thermometer

Since then, several sub-variants of Omicron have 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. The BA.5 and BA.4 variants appear to be the most contagious types of COVID-19 so far, according to the CDC. In January of 2023, a new Omicron variant called XBB.1.16 was reported and labeled as “one to watch” by the WHO.

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

Your chances of getting any variant of COVID-19 are greatest if you haven't gotten the COVID-19 vaccine. It's still possible to get the virus if you've been vaccinated (breakthrough infection), but your symptoms should be milder and your chances of having to go to the hospital are much less.

Several other things raise your risk of getting very sick from COVID-19, including

  • Older age
  • A weakened immune system
  • Other health conditions, such as obesity, diabetes, heart failure
  • Smoking, whether currently or in the past

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:

  • Runny nose
  • Cough
  • Headache
  • Mild or severe fatigue
  • Sore throat
  • Sneezing

But other common COVID-19 symptoms, such as cough, fever, and loss of smell or taste, are still important signs to watch out for in case of any COVID-19 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.

Omicron symptoms day by day

A 2020 study from the University of Southern California found that COVID-19 symptoms tend to come in this order:

  • Fever
  • Cough
  • Muscle pain and headache
  • Nausea and vomiting
  • Diarrhea

If your symptoms follow this pattern, you may want to take a COVID-19 test, seek care, and begin to self-isolate.

How long do you stay contagious with Omicron?

This variant has a shorter incubation time than those that came before itabout 3 days. If you have it, you can spread the virus to others from 1-2 days before your symptoms start until 2-3 days after they've cleared up. Even if you never show symptoms, you can still be contagious. Ten days after your symptoms begin or you test positive for COVID-19, you should no longer be contagious, as long as you're feeling better and your fever has stopped.

Studies show that the incubation period for Omicron is 3.42 days. This is shorter than the ones for the Alpha, Beta, and Delta variants.

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 shows that a previous infection only gives a 19% protection rate. It puts the chances of getting reinfected 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 weeks or months after the first illness has passed.

Omicron spreads more easily than earlier variants of COVID-19, including Delta. Researchers think this is mostly because this strain is better able to get around people's immune defenses, even if they've been vaccinated.


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 and 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 a slower increase in the number of BA.2 cases.

Early studies show that current vaccines and boosters seem to work at least against this variant, protecting against a first infection as well as against serious illness.

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 number of countries and cases linked to these variants has 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 evade virus-fighting antibodies from previous infections with COVID-19.

BA.5 subvariant. 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 of past variants. They include:

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

XBB subvariant. This subvariant is a combination of two BA.2 strains. It has mutations that help it evade immunity better than other variants. It also attaches more tightly to cells, making it easier to spread. It arose in mid-2022 and quickly became the cause of a majority of COVID-19 cases in the U.S. But it didn't cause a big jump in the number of cases. Because it has so many mutations, you could easily be reinfected with this one if you already had COVID-19 caused by another strain of the virus.

EG.5 or Eris subvariant. This descendant of the XBB subvariantfirst appeared in February of 2023. And by August of that year, it had become the most common and fastest-spreading subvariant in the U.S. While it spreads rapidly, experts have found that it's not more severe than strains that came before it.

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 this 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.

Researchers continue to look at how well current COVID-19 treatments help with Omicron cases. Because of the genetic changes in this 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.

How long does Omicron last?

This variant has an incubation period of just over 3 days. If you have Omicron or any variant of COVID-19, you will likely have symptoms for a couple of weeks. You're contagious from 1-2 days before your symptoms start until 2-3 days after they're gone. You can be contagious even if you don't have symptoms. You shouldn't be contagious anymore about 10 days after you first have symptoms or a positive COVID-19 test, as long as you're not having symptoms or a fever.

The BA.4 and BA.5 variants are close enough to the original Omicron virus, and 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.

Omicron booster

In October of 2022, the FDA authorized updated booster COVID-19 vaccines. These are bivalent vaccines, which means that they target both the original strain of the virus and the Omicron BA subvariants. You get this booster as a single dose.

If you’re an adult, you can get your booster as soon as 2 months after your most recent COVID-19 vaccine. But to get the maximum benefit, it’s best to wait at least 6 months when the antibody levels from your vaccine have gone down. If you’ve had COVID-19 recently, wait for 3 months from the date you first had symptoms or your positive test result if you didn’t have symptoms.

You can get the booster at the same time as any other vaccines you may need, including the flu vaccine. 

Visit the CDC website to see current booster recommendations for people aged 65 and older, children between the ages of 6 months and 5 years, and those with weakened immune systems.

When you get your booster, you may have side effects that include:

  • Soreness at the site of injection
  • Slight fever or chills
  • Body aches
  • Headaches
  • Tiredness

These side effects are likely to be mild and should go away within a few days.

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

Get vaccinated. Vaccines are still the best public health step to protect people against 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 any variant of COVID-19 when there is a threat 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.

Omicron is a variant of SARS-CoV-2, the virus that causes COVID-19.

  • It first appeared in November 2021 and quickly became the dominant variant around the world.
  • It spreads faster than previous COVID-19 variants but causes less severe illness.
  • Its symptoms are similar to those of other variants of this virus.
  • The currently available bivalent booster vaccines target Omicron subvariants.
  • To protect yourself from Omicron, get the COVID-19 vaccine and boosters, wear a high-quality mask, and practice social distancing in high-risk situations.

What is Omicron?

Omicron is a variant of SARS-CoV-2, the virus that causes COVID-19. A short time after it was identified, it became the dominant variant around the world.

Is Omicron a mutation?

All viruses mutate (or change) over time. Some of these changes don't alter the virus much. But others affect how they operate: They may help them adapt to the immune defenses of their host organisms so they can continue to spread. Or they can make the illness they cause more severe or harder to treat. The virus that causes COVID-19 has mutated several times since it first appeared. This means that there are several different variations or lineages that people can catch and spread to others.

Why is Omicron serious?

The incubation period for this variation of the virus is very short. You're contagious as soon as the day after you've been infected and before you have any symptoms. This makes it easy for someone to spread the illness to many other people very quickly before they realize they're sick and start to isolate themselves.

When did Omicron start?

The Omicron variation was first identified in late November 2021. The first case in the U.S. was confirmed one week later.