Viruses are continuously mutating to evolve. When a virus develops one or more mutations, it is referred to as a variation of the original virus or a variant. As of now, multiple variants of the virus that cause the coronavirus illness 2019 (COVID-19) have been identified.
How does the COVID-19 virus replicate?
As obligate intracellular parasites, viruses are dependent on the machinery of a host cell for proliferation. There are six fundamental steps that are required for viral replication.
Viral particle attachment
Proteins on the capsid or phospholipid envelope of the virus engage with specific receptors on the host cell’s surface to form an attachment. This specific interaction is required for viral entry into host cell and defines a virus’s host range.
Penetration of host cell membrane
Attachment of the viral particle to specific host cell receptors causes conformational changes in viral capsid proteins or the lipid envelope, resulting in the fusion of viral and host cellular membrane. This fusion of membranes enables the entry of the viral particle into the host cell. Some DNA viruses may also enter the host cell via a different mechanism known as receptor-mediated endocytosis.
Uncoating of the viral particle
Viral enzymes or host enzymes remove and destroy the viral capsid, releasing the viral nucleic acid into the host cell environment.
Upon release of the viral nucleic acid into the interior of the host cell, amplification of the viral genetic material and production of the viral proteins takes place. This process allows for the generation of the “raw material” for subsequent formation of new virus particles.
It is during the process of genetic material amplification that the virus can acquire mutations. These random errors that occur may or may not result in an increase in virulence of the virus.
Assembly and release of viral particles
The newly synthesized viral proteins and genetic material are then packaged into viral particles, also known as virions, that are ready for release from the host cell.
These virons, potentially carrying new variants of the virus, are then released via either lysis of the infected host cell or by budding off from the surface of the host cell.
What are the types of COVID-19 variants that have been detected?
In December 2020, the Beta variation was identified as a variant of concern after being discovered in South Africa. There is some evidence that its global frequency is declining as the Delta version takes control. Beta has a K417N mutation in addition to three of the changes seen in the Alpha (or Alpha plus) variety (E484K, N501Y, and D614G), which may enable the virus to resist neutralizing antibodies produced by vaccination or prior infection. It is expected to be 50% more transmissible than prior versions, however there is little evidence that Beta is linked to more severe illness.
Gamma, a variant of concern designated in January 2021, was originally found in Brazil. It has the E484K, N501Y, and D614G mutations, as well as several other concerning variations. It also has a K417T gene, which is related with greater binding to human cells and may facilitate viral propagation, and a H655Y genetic defect, the function of which is still unclear.
According to research reported recently in Science, the Gamma variant may be 1.7 to 2.4 times more transmissible than non-variants of concern, while people who have recovered from COVID-19 have only 54 to 79% protection against reinfection with the Gamma variant particularly in comparison to other variants. The good news is that current COVID-19 vaccinations appear to be effective.
The Delta variation was first discovered in India in May 2021. Delta carries the D614G mutation, as well as numerous other mutations not found in other variants of concern. These include a L452R mutation, which is known to increase infectivity, a T478K mutation, which is thought to help the virus avoid recognition by the immune system, and a P681R mutation, which is linked to an increased ability to cause severe disease. There have also been reports of a ‘Delta plus’ variety, which was discovered in Nepal and has an extra K417N mutation.
This variant has been found to be approximately twice as infectious as previous variants and has the potential to cause more severe disease. Unvaccinated individuals are at the highest risk of suffering from severe symptoms. Vaccinated individuals are still susceptible to infection, with or without symptoms, and can still transmit the virus to others. However, the ability of an infected individual to transmit the virus to others appears to be reduced if he or she has been vaccinated previously.
The first verified Omicron infection was discovered in November, 2021, following a surge in COVID-19 cases in South Africa. It has been authenticated at multiple sites globally, including areas of North and South America, Europe, Africa, Asia, and Australia. Omicron contains several mutations, some of which are alarming. These include the N501Y, D614G, K417N, and T478K mutations, which are also prevalent in other variations of concern, as well as a slew of others that have yet to be identified.
The B.1.1.529 variation spreads faster than the original virus and the delta variant, but appears to induce less severe sickness. People who are fully vaccinated may still get infected by the virus and transfer it to others unknowingly. BA.1, BA.2, and BA.3 are three significant offshoots (sublineages) of Omicron. According to the CDC, BA.2 accounted for approximately 55% of COVID-19 infections that underwent genetic sequencing in the United States.
What about ‘stealth’ BA.2 Omicron?
BA.2 is a subvariant of Omicron, sometimes also referred to as “stealth Omicron.” According to the World Health Organization, it is currently the prevalent strain of COVID-19 worldwide and the most transmissible version of the virus to date. BA.2 is not thought to be more severe than other varieties of Omicron, but because of the large increase in the number of cases, there has been an increase in hospitalizations in nations all over the world. The relaxation of public health restrictions, such as mask wearing and physical separation, is also contributing to the spread of the virus in many nations.
Nonetheless, COVID-19 vaccinations continue to provide excellent protection against severe sickness and mortality after infection, including infections by Omicron.
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