Omicron variant: What we know about this COVID-19 strain

Updated Mar. 15, 2022

The omicron variant of COVID-19 has become the dominant strain of the virus circulating in the U.S. and the rest of the world. It's more easily spread than previous strains because it has more mutations than any other variant so far. Many of the mutations are in the spike protein, which relates to how the virus is spread.

If you've been exposed to someone with the virus or have COVID-19 symptoms and are waiting for a test or your results, stay home and isolate from others.

Learn more about when you should get tested

You can also reach out to our experts using UC Davis Health’s convenient Telehealth Express Care for urgent needs or extended-hours video visits. Express care services are open Monday – Friday, 8 a.m. to 8 p.m. and Saturday – Sunday 9 a.m. to 6 p.m.

Read more: UC Davis Health infectious disease experts answer questions more about omicron

All of the variants, including delta and omicron, cause similar COVID-19 symptoms, including cough, fever and fatigue. There is some evidence that fewer people with omicron lose their taste and smell. Omicron is also less likely to cause severe disease such as pneumonia that may require treatment in the hospital.

In fully vaccinated and/or boosted people, omicron symptoms tend to be mild. In unvaccinated people, symptoms may be quite severe, possibly leading to hospitalization or even death.

Omicron is also more likely to cause symptoms even if you've been exposed or tested positive in the past.

See which COVID-19 symptoms you should watch for

Most people who test positive with any variant of COVID-19 typically experience some symptoms for a couple weeks. People who have long COVID-19 symptoms can experience health problems for four or more weeks after first being infected, according to the Centers for Disease Control and Prevention (CDC).

The new omicron variant BA.2 appears to be about 50% more transmissible than the original omicron strain BA.1. Preliminary data suggests BA.2 symptoms are similar, and it causes the same severity of disease. However, it's affecting younger people more.

We don't know how common reinfection is, but there are reports that several people have been infected with omicron BA.1, and within a month infected with omicron BA.2. It appears that this version of omicron is either so much more highly infectious that it can overcome vaccine or previous infection immunity, or it can evade immunity due to the mutations that it has.

To protect yourself, getting COVID-19 vaccines are still important. The second most important thing is masking. Wearing an N95 will provide the best protection against these new variants.

According to the CDC, omicron likely spreads more easily than the original COVID-19 virus. It appears to be much more contagious compared to the delta variant, as it quickly became the dominant strain in the U.S. The CDC said it expects that people can spread omicron even if they’re vaccinated or don’t have symptoms.

Omicron is more likely to cause less severe illness compared to other variants. For example, preliminary data suggest that infection with omicron results in hospitalization at about half the rate compared to infection with delta. Given how infectious omicron is, it’s important for everyone to take all precautions, including getting vaccinated and wearing a mask.

Since the omicron variant is so new, health experts do not have a clear idea how effective the vaccines are in preventing illness. There's a potential that COVID-19 vaccines might not be as effective with new variants. However, the more antibodies a person has, the more protected they will be. That’s why everyone is encouraged to get a COVID-19 booster shot once you're eligible.

Preliminary evidence suggests that vaccines are less effective against the spread of omicron, compared with delta. But vaccines still protect well against serious illness such as hospitalization.

At-home COVID tests, also known as rapid antigen tests, are useful because they provide quick results. Tests can be purchased without a prescription and are available at pharmacies and stores. At-home test brands include BinaxNOW and iHealth. You can also sign up to get four free COVID test kits that are mailed to you from the federal government.

If you've been exposed to someone with COVID-19 or are having symptoms, at-home tests can give you a good sense of whether or not you have an infection. These tests are pretty reliable, but they're not perfect.

  • If you have COVID-19 symptoms and test negative, you still might have COVID-19 and should stay away from others.
  • If you have COVID-19 symptoms and test positive, you can trust that positive result. You can always request a diagnostic or PCR test from your physician to confirm that result. If you test positive, isolate for at least five days, as recommended by the CDC.

Watch this video for tips on using at-home tests

Learn what to do if you test positive for COVID-19

See how at-home rapid COVID tests can help families stay safe

Several studies, including one from UC Davis, indicate how effective masks can be in protecting yourself and others. It’s important to remember that you may be asymptomatic and not know you are infected but still able to spread COVID-19. Wearing a mask in these situations helps protect vulnerable people you could unknowingly infect.

Mask guidance continues to change, depending on rates of spread within communities, as well as the levels of vaccination and immunity people have from both vaccination and infection. Even if masking is not required, consider wearing a mask in public indoor spaces if you or people you live with are at high risk for severe disease.

Consider upgrading your face masks to N95s or KN95s if you want more protection. Cloth masks reduce the risk of infection by about 50%. This is compared to surgical masks that reduce the rate of infection by about 60-70%, and greater than 80% for N95s.

Learn more about which masks are best to protect against omicron

Yes. It’s important to know if you're infected with COVID-19 for three reasons:

  1. If your illness gets worse, you’ll want to know so you can take advantage of COVID-19 treatments.
  2. You need to know whether to isolate so you can reduce your chances of infecting others, especially those who are more vulnerable to severe COVID-19.
  3. You will want to notify anyone you were recently in contact with so they can monitor their symptoms and get tested if needed.

Most likely. Unfortunately, omicron is so easily spread that even those who are fully vaccinated and boosted may get the illness. If you know you had contact with an infected person, particularly in a higher-risk situation (such as an indoor space for a longer period with others who weren’t masked), testing is advised. You should also quarantine, watch for COVID-19 symptoms, stay away from others in your home, and wear a mask. If you test positive, then you should isolate.

However, if you were in a situation where people were outside, masked and distanced, the risk of infection is much lower. Instead of testing right away, you could monitor for COVID-19 symptoms and get tested if any develop.

Learn more about the difference between quarantine and isolation

Although it can vary, people are generally contagious between 1-3 days before omicron symptoms show.

The more people who are infected, the more likely we are to see new variants. The message from health experts remains that everyone should be vaccinated against COVID-19. Every time COVID-19 infects someone, there’s a chance for more mutations, which can allow the virus to keep spreading. Stay vigilant and get vaccinated if you haven’t already.

Learn how to schedule your COVID-19 vaccine at UC Davis Health