Are there different strains of coronavirus?

Medically reviewed by Neka Miller, PhD. Updated January 25, 2021. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.


As the pandemic continues, one area of study some researchers are investigating is the potential for a newer (possibly more dangerous) strain of the novel coronavirus. So are there different strains of the coronavirus—and what does it mean for those of us in the midst of a pandemic? Here, we’ll tackle these questions—but first, let’s discuss what “coronavirus” refers to.


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What is a coronavirus?

Although many people use “coronavirus” to refer to the novel coronavirus responsible for the current COVID-19 outbreak, “coronavirus” in general refers to a broad family of viruses. These viruses can infect birds and mammals, including humans. Coronaviruses get their name from the Latin word for crown—“corona”—due to the crown-like spikes that naturally appear on their surface.

Human coronavirus species were initially discovered in the 1960s. Since then, there have been seven known coronaviruses that can be transmitted among people.

  • SARS-CoV is the coronavirus known for causing severe acute respiratory syndrome (SARS).
  • MERS-CoV is the coronavirus that causes Middle East respiratory syndrome (MERS).
  • SARS-CoV-2 is the viral strain responsible for the current COVID-19 pandemic and is also referred to as the “novel coronavirus.” What makes SARS-CoV-2 “novel”? It’s a new viral strain and has never been discovered in humans prior to late 2019. This means that no one is naturally immune to the virus, making it highly transmissible and dangerous.

The four most common human coronaviruses are 229E, NL63, OC43, and HKU1. These viruses are responsible for the common cold and similar illnesses that cause mild to moderate respiratory issues.

How many strains of coronavirus are there that cause COVID-19?

It isn't completely known how many strains of SARS-CoV-2 there are, but what we do know is that—throughout most of the pandemic—COVID-19 cases have usually been caused by a widespread, dominant variant of SARS-CoV-2 that's associated with the D614G mutation in the virus' spike protein (the spike protein allows SARS-CoV-2 to bind to human cells).

Understanding why it's called a "D614G" mutation requires a foray into molecular biology. Viruses build proteins by chaining together a sequence of different amino acid building blocks. Each of these amino acids have a single-letter abbreviation. "D" refers to the amino acid aspartate, and "G" stands for another amino acid called glycine. "D614G" means that the 614th amino acid in the virus' spike protein changed from aspartate (D) to glycine (G) via mutation. The strain of the virus with this specific mutation has become dominant.

However, research suggests that new lineages of the virus have developed, and it's likely that some of these lineages are more easily transmittable from person to person (a lineage is defined by a unique set of mutations). In particular, lineage B.1.1.7—otherwise referred to as 501Y.V1 or the "UK coronavirus variant"—has recently become the subject of increasing scientific scrutiny.

It's thought that this lineage first emerged in England in the fall of 2020, and it was first detected in November 2020. It has since spread rapidly—not just throughout England, but to other countries, as well (including the United States). What's notable about lineage B.1.1.7 is that it's significantly more transmissible than the typical form of SARS-CoV-2. Population genetic studies of the virus in England suggest that lineage B.1.1.7 spreads 56% faster compared to other lineages.

Because of how quickly viruses in this lineage can spread—and now that the lineage has spread to other parts of the world—the need for widespread vaccination has become even more urgent.

How new coronaviruses emerge

Viruses work by taking over host cells and replicating within those cells. All virus populations undergo random mutation—spontaneous changes in their genes (viruses consist of a protein core wrapped in genetic material—either DNA or RNA).

Every now and then, these mutations provide a fitness advantage to some viruses in a population—in other words, a genetic change occurs that allows some viruses to thrive more effectively. (For example, influenza viruses—responsible for the seasonal flu—change rapidly via mutations, leading to significant alterations to their surface proteins, making them harder to identify by human immune cells. This is one major reason why you need a new flu vaccine every year.) Over time, these genetic changes can become more widespread in a virus population, ultimately allowing a whole new strain to emerge.

While influenza viruses are known for mutating quickly, coronaviruses change at about a tenth of the speed according to studies, and the SARS-CoV-2 virus is on track with this estimate. SARS-CoV-2 itself was a mutation of the initial SARS virus, and this novel coronavirus has already picked up several mutations since it was originally discovered in late 2019. However, the mutation rate is in line with what experts predicted, and while various lineages have evolved, none of them (as far as we know) are significantly different from each other from the perspective of vaccine development and treatment methods.

Conclusion

Though the novel coronavirus can be broken down into different lineages, the same basic principles for controlling the spread of the virus applies to all lineages: extensive vaccination, testing widely, quarantining those who have been infected, making use of contact tracers, wearing masks, and maintaining proper social distancing practices.

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