The SARS-CoV-2 coronavirus is quite versatile, with a large number of variants and sub-variants. The omicron variant alone has over 130 sublineages.
In Europe, the omicron BA.4 and BA.5 sub-variants are currently on the rise. Why are they spreading so fast, when many people have already been vaccinated?
Omicron is better at evading the immune system
“New variants are traditionally defined as a new set of mutations thought to alter how the virus works. Typically, these variants have increased infection rates and disease severity,” said Krishna Mallela, a professor in the department of pharmaceutical sciences from the University of Colorado in the United States, said DW.
Now scientists are beginning to understand why specific mutations make variants more infectious, like omicron, or more deadly, like delta — and it comes down to how the coronavirus enters cells and how our immune system fights it.
A recent study in the United States showed that omicron is more infectious because it can better evade our immune system.
After a previous vaccination or infection, the antibodies circulate in your body and drive out the viruses. They detect the coronavirus via its spike protein, which then signals that the virus should be neutralized.
The study shows that mutations in omicron subvariants BA.1 and BA.2 alter the structure of the spike protein.
“Mutations are in places where antibodies bind to the spike protein. Mutations cause a different binding surface, which is less recognized by antibodies. This leads to evasion of antibody protection,” said Kamal Singh, immunologist from the University of Missouri. in the United States, said DW.
Essentially, your immune system is less effective at tracking down and destroying omicron virus particles. This escape is behind the huge rise in infections worldwide since omicron was first identified in South Africa in November 2021.
Why is the delta deadlier?
With all the news from omicron lately, it’s easy to overlook previous variants, like delta. Delta is the most virulent coronavirus variant, causing more severe symptoms and increased mortality in infected patients. UK statistics show that the risk of death with omicron is 67% lower than that of a delta infection.
Research has shown that delta is particularly deadly due to mutations on the spike protein, protrusions on the surface of the virus. A new US-based study has found that two mutations cause increased expression of the spike protein on the delta variant of the virus.
This is important because SARS-CoV-2 is like a thief trying to sneak into your home, or rather your cells – and it does so via spike proteins.
Its system of breaking into cells is via a protein expressed on the surface of cells in your body called ACE2. This protein is like a doorway into your cells. Normally it is closed and requires a key to open it.
SARS-CoV-2 managed to trick ACE2 into thinking it should be introduced into your cells. Essentially, it’s about duplicating your house keys.
In biological terms, the keys are the spike proteins, which bind to ACE2. Once inside, the virus replicates and spreads.
Coronavirus enters human cells via its spike proteins
For delta, more spike proteins mean a greater ability to enter cells and reproduce, leading to higher amounts of coronavirus in the body.
Mallela, the study’s lead author, explained how the mutations also affect the immune system’s ability to neutralize the virus.
“Our study found that delta reduces spike protein binding to an important class of antibodies [in the human body]. This leads to higher infectiousness rates and more severe symptoms,” he said.
Future vaccines seek to combat new variants
Coronavirus vaccines have been hugely successful, reducing mortality and severe symptoms around the world. However, new variants are likely to appear in the coming years, and they could be more transmissible and deadly.
Scientists are working hard to stay ahead of the game, developing new coronavirus vaccines that train the immune system to deal with new variants.
“There are about 220 vaccine candidates in clinical trials around the world,” Mallela said. “These updated vaccines will allow us to generate an immune response that is better suited to combat the circulating variants at the time of vaccination.”
And there is reason to be optimistic. For example, UK-based scientists recently presented a promising new vaccine that better protects against novel coronavirus variants like omicron. The study authors used new nanoparticle technology to create a vaccine that can easily be adapted to target future variants.
Edited by: Carla Bleiker