VIRUS MUTATIONS AND VARIANTS
When a virus’s structure changes as it replicates, such changes are referred to as mutations, and a virus with one or more new mutations is referred to as a variant (WHO, 2021c).
Viral mutation is the alteration of the sequence of a virus’s genetic code. Viral mutation is a normal physiologic occurrence, and viruses are constantly mutating. Where mutations are located in a virus’s genetic material determine how they alter a virus’s properties. For instance, a mutation may alter a virus so that it spreads more or less easily or so that it causes more or less severe disease (WHO, 2021c).
The majority of the time mutations are so small that they do not significantly affect how the virus behaves (Cleveland Clinic, 2021).
MEASURES TO HELP REDUCE VARIANTS
The more opportunities a virus has to spread, the more it replicates and the greater the chances for mutation. It is possible to reduce the number of variants that a virus develops. To reduce spread, and opportunity for the appearance of variants, public health measures for disease prevention (such as wearing a mask, washing hands, limiting close contact with others, and getting vaccinated) must be followed (Cleveland Clinic, 2021).
Antigenic Drift
One way that viruses can mutate is via antigenic drift. Antigenic drift refers to small changes in the genes of viruses that happen on a continual basis over time as the virus replicates. These genetic changes typically produce viruses that are closely related to each other. These viruses usually share the same antigenic properties. Thus, an immune system exposed to a similar virus will usually recognize and respond to it (CDC, 2019).
However, these small genetic changes accumulate over time and eventually cause the development of viruses that are antigenically different. When this occurs, the body’s immune system may not recognize such viruses, and illness can occur.
Antigenic viral changes are anticipated, so the composition of any vaccine must be evaluated regularly and updated as needed. Pandemics are less likely to occur with antigen drift thanks to researchers who continually monitor virus evolution and update vaccines as needed and to the gradual nature of virus replication (CDC, 2019).
Antigenic Shift
Antigenic shift is an abrupt, major change in a virus that causes the production of new proteins in the viruses that infect humans. It is typically unexpected and unpredictable. Antigenic shift leads to a new virus subtype or one that has emerged from an animal population that is so different from the same subtype of viruses in humans that most people do not have immunity to the new type of virus. When this type of shift occurs, the new viruses infect people, spread rapidly, and can lead to a pandemic (CDC, 2019).
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Variants of the COVID-19 Virus
There are multiple variants of the SARS-CoV-2 coronavirus that are different from the version first detected in China. For instance, a mutation that appeared in southeastern England in September 2020 rapidly became the most common variant of the coronavirus in the United Kingdom and has been estimated as >50% more contagious than earlier viral variants (Cleveland Clinic, 2021).
WHO LABELS FOR SARS-COV-2 VARIANTS
To assist with public discussions of variants, a group of scientists and experts convened by the World Health Organization (WHO) developed easy-to-pronounce and nonstigmatizing labels for variants of concern (VOC) and variants of interest (VOI) using letters of the Greek alphabet.
Variants of concern: A SARS-CoV-2 variant that meets the definition of a VOI (see below) and has been demonstrated to be associated with one or more of the following changes at a degree of global public health significance:
- Increase in transmissibility or detrimental change in COVID-19 epidemiology
- Increase in virulence or change in clinical disease presentation
- Decrease in effectiveness of public health and social measures or available diagnostics, vaccines, therapeutics
Variants of interest: A SARS-CoV-2 isolate whose genome has mutations with established or suspected phenotypic implications, and either:
- Has been identified to cause community transmission/multiple COVID-19 cases/clusters, or has been detected in multiple countries; or
- Is otherwise assessed to be a VOI by WHO in consultation with the WHO SARS-CoV-2 Virus Evolution Working Group
(WHO, 2021d)
Some of the SARS-CoV-2 variants identified include:
- B.1.351 (beta): This variant was identified in South Africa. It has not been known to cause more severe illnesses than earlier versions of the virus.
- B.1.1.7 (alpha): This variant was identified in England. Preliminary data suggested that this variant is more contagious than earlier versions of the virus. There have been surges of cases in locations where this new strain appeared. This variant appears to bind more tightly to the cells of the body, and it consists of 17 genetic changes from the original virus (Johns Hopkins Medicine, 2021).
- B.1.617.2 (delta): This variant was identified in India; it has two mutations in the spike protein of the coronavirus that facilitates its attachment to cells (Ellis, 2021).
Other early variants emerged in Brazil (gamma) and California (epsilon), and additional variants continue to be identified.
As long as the SARS-CoV-2 virus spreads, mutations will continue to occur and new variants will be found. Researchers will work to determine whether each variant spreads more easily, the impact it has on the severity of illness, and the effectiveness of current vaccines against the variant (Johns Hopkins Medicine, 2021).