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Healthy Tips

Quick Dose: What Is a Viral Variant?

Published September 2021

If you have ever caught a virus, like the influenza virus that causes the flu, or the rhinovirus that causes the common cold, you have likely caught a variant of the virus and not the original virus.

Viruses are not living organisms. They are very small groups of molecules often built from proteins, lipids (fats) and carbohydrates. They cannot do anything without a host cell. A virus needs other living cells to make more copies of itself, or to replicate. 

When viruses replicate, sometimes they change, or mutate. A virus that has changed from its original form is called a variant. Viral variants are normal and to be expected. The Centers for Disease Control and Prevention (CDC) uses the metaphor of a tree to describe viral variants: If the virus is a tree, each variant is a new branch of the tree. No two tree branches look or grow exactly alike, but they are part of the same tree. Likewise, variants are part of the same virus, but each one looks and/or behaves slightly differently.

Some variants can spread more easily than the original virus. Sometimes variants can be more resistant to treatments or vaccinations against the original virus. Other times, there is little difference between how a variant looks and behaves compared to the original virus.

The CDC tracks the spread of variants of COVID-19. Not all variants are cause for concern. The CDC website describes those that are considered variants of concern in the U.S.

Michael G. Ison, MD
Michael G. Ison, MD
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Professor, Feinberg School of Medicine
  • Primary Specialty Infectious Disease
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