How Do Viruses Mutate?

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A virus is a small infectious agent made up of genetic material, either DNA or RNA. They can only multiply inside the cells of other living things. The cell they multiply in is called the host cell.

When a virus invades the host cell, it essentially "rewrites" the instructions for the way the cell operates. While occupying its host, a virus replicates (makes copies of itself) so that it can survive until moving on to the next. As viruses move from person to person in search of survival, they can mutate—or change—over time.

This article discusses how viruses mutate, how mutation can affect vaccines, and what viral mutation means as it relates to COVID-19.

Lab scientist studying virus mutation

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How Do Viruses Mutate?

Viruses survive by making hundreds, even thousands, of copies of themselves, so errors in how those copies are made are a natural part of the process.

There are three possible outcomes when a virus mutates:

  • Nothing happens
  • The virus gets weaker
  • The virus gets stronger

Typically, mutations don't significantly impact symptoms associated with a particular virus or the way it spreads. However, this can vary from virus to virus.

How Quickly Do Viruses Mutate?

The rate at which viruses mutate depends on a variety of factors, such as their genetic makeup, which is why rates differ among viruses.

Further, it can be difficult to accurately measure the rate of mutation because some mutations don't allow the virus to survive, and therefore they cannot be studied.

How Does This Affect Vaccines?

Viruses mutate at different rates and can affect vaccines differently, depending on the virus.

Influenza (the flu), for example, has a much higher mutation rate than SARS-CoV-2, the virus that causes COVID-19, which is why a new flu vaccine is produced each year.

What Does This Mean for COVID-19?

According to the World Health Organization (WHO), the COVID-19 vaccines provide protection against new virus mutations or variants. This is due to the antibodies produced by the immune system as a result of the vaccine. Therefore, viral mutations should not make vaccines ineffective.

Variants are versions of the virus that have mutated to a point that the difference is easily identified during genetic sequencing done in research labs. The current COVID-19 vaccines are still effective against the currently known variants, but their effectiveness is not as strong as with earlier versions of the virus.

Variant Classifications

The Centers for Disease Control and Prevention (CDC) classifies coronavirus variants into four categories. How a variant is classified depends on classified based on their level of threat to the population.

  • A variant being monitored (VBM) poses no significant threat to the public.
  • A variant of interest (VOI) has "specific genetic markers" that make them more of a threat to the public.
  • A variant of concern (VOC) shows evidence it spreads more easily, causes more severe illness, and evades existing COVID-19 treatments.
  • A variant of high consequence (VOHC) makes COVID-19 treatments less effective and affects more vaccinated people.

Mutations vs. Variants vs. Strains

These terms are often used interchangeably, but they have different meanings. Think of them as building blocks—mutations lead to variants and variants lead to strains.

Here are the specific breakdowns:

  • Mutations: Change the way the genetic code of a specific virus is written, but have little to no effect on characteristics of the virus
  • Variants: Includes one or more mutations of a virus that have survived and replicated often enough to be identified as a variant
  • Strains: Occur when a virus changes so much that it has characteristics that separate it from versions of the virus that have occurred previously


Viral mutation is a common occurrence and not a cause for major concern. It can, however, lead to variants and eventually even new strains of a virus. Understanding how viruses evolve can inform preventive strategies, such as vaccination.

The COVID-19 vaccine has proven to be effective at reducing an individual's risk for becoming infected with the virus, thus decreasing chances for the virus itself to survive and multiply. Further, the COVID-19 vaccines have proven to be protective against the variants that have emerged so far.

A Word From Verywell

The topic of viral mutations and variants can conjure up fear for many, but in reality, it's a normal scientific process. Simply learning about the differences between viral mutations, variants, and strains can equip you with the knowledge to live with a healthy amount of caution, but not in fear.

Frequently Asked Questions

  • How do new variants of COVID-19 occur?

    New variants of COVID-19 occur when a viral mutation becomes so common that it is easily detectable based on its genetic code and other characteristics.

  • How often do viruses mutate?

    The rate at which viruses mutate depends on a variety of factors, such as their genetic makeup, which is why rates differ among viruses.

  • Do vaccines protect against all the variants of a virus?

    The efficacy of a vaccine against certain variants of a virus depends on the virus itself. The current COVID-19 vaccines have been shown to reduce disease severity as well as hospitalization and death rates among all the variants.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Tufts University. How viruses mutate and create new variants.

  3. Peck KM, Lauring AS. Complexities of viral mutation rates. J Virol. 2018;92(14):e01031-17. doi:10.1128/JVI.01031-17

  4. Manzanares-Meza LD, Medina-Contreras O. SARS-CoV-2 and influenza: a comparative overview and treatment implicationsBol Med Hosp Infant Mex. 2020;77(5):262-273. doi:10.24875/BMHIM.20000183

  5. World Health Organization. The effect of virus variants on the COVID-19 vaccines.

  6. Centers for Disease Control and Prevention. SARS-CoV-2 variant classifications and definitions.

  7. Mascola JR, Graham BS, Fauci AS. SARS-CoV-2 viral variants—tackling a moving targetJAMA. 2021;325(13):1261–1262. doi:10.1001/jama.2021.2088

By Teresa Maalouf, MPH
Teresa Maalouf is a public health professional with six years of experience in the field. She has worked in research, tobacco treatment, and infectious disease surveillance. Teresa is focused on presenting evidence-based health information in a way that is clear and approachable.