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Why Viruses Mutate, Explained by an Infectious Disease Expert

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COVID-19 virus with purple COVID-19 variant

You’ve probably heard a lot about COVID-19 variants. Infectious Disease Expert Dr. Leyla Best, UnityPoint Health, identifies three things you should know about virus changes, especially during the COVID-19 pandemic.

How Do Viruses Evolve So Quickly?

Viruses aren’t living things. They need a host to survive – like the cells in your body. Once a virus enters your body, it reproduces and spreads. The more a virus circulates in a population of people, the more it can change. All viruses change but not always at the same rate.

“The rate of change varies from virus to virus. Some change very fast, such as the influenza virus. That is why we get a new flu vaccine every year. SARS-CoV-2, the virus that causes COVID-19, has taught us a lot. Current research suggests it changes at a slower rate than influenza,” Dr. Best says.

Because viruses are always changing, it's very important to stay up-to-date on all vaccines.

What's the Difference Between Mutations, Variants and Strains?

  • Mutation. When a virus replicates, and the end copy has differences (in DNA or RNA), those differences are mutations.
  • Variant. When you accumulate enough mutations, you get a variant.
  • Strain. When you can prove a variant truly has new biologic capabilities, then you can call it a strain.

“With COVID-19, the changes to the virus are currently called variants. More research is needed to determine if any of the variants can be called a strain. In the spring of 2021, the World Health Organization (WHO) created a new system to name COVID-19 variants using Greek letters. This avoids the use of locations, which can be stigmatizing to a country. The CDC identifies four main variants of concern – the alpha (B.1.1.7, first detected in the UK), the beta (B.1.351, first detected in South Africa), the gamma (P.1, first detected in Brazil) and the delta (b.1.617.2, first detected in India),” Dr. Best says.

The CDC says no variants of high consequence have been identified in the United States at this time. 

What is the Delta Variant of COVID-19?

The delta variant of COVID-19 is the newest variant of concern. It was first identified in India in December of 2020. Early research suggests delta may be more contagious than other COVID-19 variants. It is also now the dominant variant circulating in the United States and has been identified in all 50 states.

“Self-reporting data from the U.K. identify cold-like symptoms, including headache, runny nose and a sore throat are more common with the delta variant than the more traditional COVID-19 symptoms of loss of smell, shortness of breath, fever and cough,” Dr. Best says.

Researchers say the vaccines remain our biggest tool against warding off the COVID-19 variants, including the delta variant. If you received an mRNA vaccine (Pfizer or Moderna) make sure you’ve received both doses, so you’re fully protected.

"Delta won’t be the last variant of COVID-19 we see. That’s because every time the virus jumps to a new person, its chance of mutation increases. If the virus keeps running into vaccinated people, it hits a wall and can’t keep spreading. Decreasing the number of infections in a community is the best way to prevent new variants from developing,” Dr. Best says.

Why is it Important to Focus on the Impact of the Virus’ Change?

“What matters is the impact the changes have on the virus itself. So, some viruses might have a few differences – a few mutations – but there are no noticeable changes to the virus. Sometimes viruses can have mutations that give the virus an advantage, whether that’s a better attachment to cells or the ability to replicate faster. Mutations can also result in disadvantages for the virus, lowering the ability to attach to cells or taking longer to reproduce,” Dr. Best says.

The important things for scientists to identify about changing viruses, like the virus that causes COVID-19, is how the change impacts people, if the vaccines still work and if tests can still identify the active virus.

“For COVID-19, researchers are interested in the alpha, beta, delta and gamma variants, because they seem to be associated with either higher transmissibility. Scientists are keeping a close eye on the variants to determine if the vaccines, or the treatments, are less effective. At this point, current PCR testing and rapid testing can detect all COVID-19 variants,” Dr. Best says.

What Causes Viruses to Mutate?

Virus changes are associated with three things. First, sometimes a change in a virus is a pure error.

“A good analogy about virus changes is that it’s like copying a manuscript and, at some point, you're going to have a typo,” Dr. Best says.

Another reason a virus might change is because of pressure from select cells in the body.

“This hypothesis emerged regarding some of the COVID-19 variants. It states if a virus infects a person who doesn’t have a very strong immune system, for example, someone with cancer, then the body is not able to clear the virus very well. Then the virus can say, ‘Hey, how are you going to attack me and make changes based on that?’,” Dr. Best says.

The creation of a vaccine for any new virus could also cause additional mutations.

“Let’s explain this concept a little further. Any virus will keep trying to change, so it can continue to spread. With all vaccines, the more quickly people get vaccinated the better. The slower vaccination happens, the higher the chance of having mutations in the virus and the appearance of more variants. And, as we are seeing with the delta variant, the more the virus can spread in the community."

In order to keep viruses in check, everyone must do their part by getting vaccinated, and scientists must work together around the world to track emerging variants.


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