Which coronavirus variants are circulating in the U.S.?

As of May 2025, the top 5 variants circulating in the U.S. are all lineages of the Omicron variant and include:

• LP.8.1 (73%)
• XFC (10%)
• XEC (4%)
• LF.7.7.2 (3%)
• LF.7 (2%)

These estimates are reported by the CDC on the COVID Data Tracker.

The original Omicron variant, first identified in Botswana and South Africa in late November 2021, is no longer circulating. Other variants are currently circulating worldwide, and new variants may occur over time.

There are many different variants of the COVID-19 virus at any one time. In the U.S., sequence-based strain surveillance is ongoing in academic, state and public health government (CDC) institutions as well as in the World Health Organization (WHO). This research helps to support understanding the variant types and virulence, vaccine effectiveness and future pandemic preparedness.

How dangerous are the coronavirus COVID-19 variants?

All viruses can mutate which leads to changes in their internal genetic code, creating "variants." Mutations are an expected part of the virus life-cycle, and not all variants are dangerous or harmful.

Scientists are researching how the new variants may alter COVID-19 disease, natural immunity, and the effect on vaccine effectiveness.

• Some mutations of the coronavirus have been shown to be more contagious or to cause more serious COVID-19 illness.
• Variants may affect the effectiveness of the COVID-19 vaccines. However, experts state that the virus would need to develop multiple mutations in the spike protein to evade immunity induced by vaccines or by natural infection.
• A person's natural immunity from a previous COVID-19 infection could be affected by variants. This could lead to a spike in new cases. Variants theoretically may also alter the results of lab tests used to detect the virus or antibodies.

How do mutations affect vaccines?

Mutations can make vaccines hard to develop because of the change of the genetic footprint of the virus. Viruses often naturally mutate.

One example is the flu vaccine. New strains of influenza often appear worldwide each year, and those strains are incorporated into a new vaccine each flu season. Because the influenza vaccine gets a reboot each year, and it’s protective effect wanes over time, you need a yearly vaccine for protection against influenza.

But other viruses do not mutate so quickly. For example, the measles is slow to mutate. To protect yourself or your child from measles, one set of shots, typically given in childhood, is protective for a lifetime.

COVID-19 is a highly contagious viral infection due to the SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) virus. The coronavirus is a long virus microscopically with 30,000 nucleotides and is twice the size of the flu virus. Coronavirus is an RNA virus, as are the flu and measles virus. Variants appear to have developed mutations in the spike protein of the coronavirus. The spike protein is the part that helps the virus to attach to infect human cells.

As of now, studies suggest that vaccination with the currently available vaccines in the U.S. recognize these SARS-CoV-2 variants. As the SARS-CoV-2 virus mutates over time, further vaccine updates may be needed, similar to how the influenza vaccine is updated yearly.

Which COVID-19 vaccines are available in the U.S.?

There are several COVID-19 vaccines available in the U.S made by either Pfizer and BioNTech, Moderna or Novavax.

Pfizer and BioNTech - mRNA vaccines.

• Comirnaty is the brand name of the COVID-19 vaccine made by Pfizer and BioNTech which is approved for adults and adolescents 12 years and older.
• The Pfizer-BioNTech COVID-19 vaccine has Emergency Use Authorization (EUA) for children aged 6 months through 11 years.

Moderna - mRNA vaccines.

• Spikevax is the brand name of the COVID-19 vaccine made by Moderna which is approved for use in adults and adolescents aged 12 years and older.
• The Moderna COVID-19 vaccine has Emergency Use Authorization (EUA) for children aged 6 months through 11 years.
• On May 30, 2025, the FDA approved mNEXSPIKE vaccine to prevent COVID-19 in individuals who have been previously vaccinated with any COVID-19 vaccine and who are 65 years of age and older, OR 12 years through 64 years of age with at least one underlying condition that puts them at high risk for severe outcomes from COVID-19. Moderna expects to have mNEXSPIKE available for the 2025-2026 U.S. respiratory virus season.

Novavax - protein adjuvant (non-mRNA vaccine).

• The Novavax COVID-19 vaccine is a protein subunit vaccine that may be used to help the body form immunity to SARS-CoV-2, the virus that causes COVID-19. It can be used in adults and children 12 years of age and older. Novavax is available for use under the FDA's Emergency Use Authorization (EUA). It is not authorized for use in children younger than 12 years of age.
• On May 19, 2025, the FDA approved Nuvaxovid (COVID-19 Vaccine, Adjuvanted), a protein-based, non-MRNA vaccine for active immunization to prevent coronavirus disease 2019 (COVID-19) in adults 65 years and older, and for individuals 12 through 64 years who have at least one underlying condition that puts them at high risk for severe outcomes from COVID-19. Nuvaxovid is an updated version of the Novavax COVID-19 Vaccine formulated to target the JN.1 variant. Novavax expects to have Nuvaxovid available for the 2025-2026 U.S. respiratory virus season.

These vaccines do not contain SARS-CoV-2, the virus that causes COVID-19 and cannot give you COVID-19. These vaccines will not treat an active COVID-19 infection.

Like any vaccine, these vaccines may not protect every person but can help prevent severe illness, hospitalization and death.

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How do the COVID-19 vaccines work?

mRNA

The messenger RNA (mRNA) vaccines encode a form of the spike (S) protein of SARS-CoV-2 virus. The vaccine teaches the cells to make a piece of the spike protein, which triggers an immune response to help prevent illness if later exposed to the virus. The partial piece of the spike protein cannot cause COVID-19 disease.

Commonly reported side effects with mRNA vaccines include injection site pain or swelling and flu-like symptoms such as fever, chills, tiredness, muscle and joint pain, and headache. These side effects subside in 24-48 hours in most patients. In some cases, side effects may be worse after the second dose than the first dose.

Severe allergic reactions (anaphylactic reactions) are rare but have been reported. These reactions can be treated, and most patients with allergies can still get the vaccine. It is recommended you do not use the vaccine if you have had a severe allergic reaction to any of the ingredients in the vaccine you receive, or to a previous dose of the vaccine.

After the mRNA COVID19 vaccines were approved or authorized, increased risks of myocarditis and pericarditis (inflammation of heart tissues) were reported. The observed risk has been highest in males 12 through 24 years of age.

You should seek medical attention right away if you or your child has any of the following symptoms after receiving a COVID-19 vaccine, especially in the first 2 weeks after receiving the vaccine:

• Chest pain
• Shortness of breath
• Feelings of having a fast-beating, fluttering, or pounding heart

Related: mNEXSPIKE FDA Approval History

Protein adjuvant

Novavax and Nuvaxovid are protein subunit vaccines and are based on more traditional vaccination approaches compared to mRNA vaccines. An adjuvant is a substance added to a vaccine to boost your immunity to the vaccine ingredients which can lead to a stronger response.

The Novavax COVID-19 Vaccine, Adjuvanted 2024-2025 was formulated to target JN.1, the updated 'parent strain' of variants, according to Novavax. Novavax COVID-19 is available for use under the FDA's Emergency Use Authorization (EUA). It is not authorized for use in children younger than 12 years of age.

Nuvaxovid is an updated version of the Novavax COVID-19 Vaccine formulated to target the JN.1 variant and approved in May 2025. Nuvaxovid is engineered using recombinant nanoparticle technology to create copies of the surface spike protein of SARS-CoV-2, which serve as the antigen.

Novavax’s patented saponin-based Matrix-M adjuvant is used to enhance the immune response and stimulate high levels of neutralizing antibodies. Saponins are naturally occurring compounds in the bark of the Quillaja saponaria (Soapbark) tree.

Commonly reported adverse reactions (>10%) include injection site tenderness or pain, headache, fatigue, muscle pain, malaise, nausea / vomiting, fever, and joint pain.

Related: Nuvaxovid FDA Approval History

How long does the COVID vaccine last?

COVID-19 is still spreading throughout the U.S., and is expected to continue. The duration of protection from the vaccines is not fully known yet, but Pfizer / BioNTech and Moderna have reported that immunity lasts at least 6 months with their vaccine. Pfizer has noted that their vaccine remains up to 91% effective.

This is not all the information you need to know about COVID-19 and COVID-19 vaccines for safe and effective use and does not take the place of your doctor’s directions. Review the full product information and discuss this information and any questions you have with your doctor or other health care provider.

References

• Variant Proportions. COVID data tracker. US Centers for Disease Control and Prevention (CDC). Accessed June 5, 2025 at https://covid.cdc.gov/covid-data-tracker/#variant-proportions
• Pfizer-BioNTech Announce Positive Topline Results of Pivotal COVID-19 Vaccine Study in Adolescents. Press release. at https://www.pfizer.com/news/press-release/press-release-detail/pfizer-biontech-announce-positive-topline-results-pivotal
• About Variants of the Virus that Causes COVID-19??. US Centers for Disease Control and Prevention (CDC). https://www.cdc.gov/coronavirus/2019-ncov/index.html
• FDA Issues EUA for Moderna COVID-19 Vaccine. Drugs.com. MedNews. Accessed April 5, 2021 at https://www.drugs.com/news/fda-issues-eua-moderna-covid-19-vaccine-94728.html
• Pfizer and BioNTech Confirm High Efficacy and No Serious Safety Concerns Through Up to Six Months Following Second Dose in Updated Topline Analysis of Landmark COVID-19 Vaccine Study. Press release. https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-confirm-high-efficacy-and-no-serious
• What COVID-19 variants are going around in December 2024. Nebraska Medicine. Accessed Dec. 17, 2024 at https://www.nebraskamed.com/COVID/what-covid-19-variants-are-going-around

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