In Europe, omicron BA.4 and BA.5 sub-variants are currently on the rise. Why are they spreading so quickly despite the fact that so 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 that are thought to change how the virus works. Typically these variants lead to increased rates of infection and increased severity of disease,” Krishna Mallila, a professor in the Department of Pharmaceutical Sciences at the University of Colorado in the US, told DW. .
Scientists are now beginning to understand why certain mutations cause variants to be more infectious, like omicron, or more deadly, like delta — and it has to do with how the coronavirus gets into cells, and how our immune system fights it off.
A recent study from the United States showed that omicron is more contagious because it can better evade our immune system.
After a vaccination or a previous infection, the antibodies circulate in your body and hunt down the viruses. They detect the coronavirus via the spike protein, which then signals the virus to be neutralized.
The study showed that mutations in the omicron sub variants BA.1 and BA.2 alter the structure of the spike protein.
“Mutations occur where antibodies bind to the spike protein,” said Kamal Singh, an immunologist from the University of Missouri. “The mutations cause a different binding surface, which the antibodies do not recognize less. This results in avoidance of antibody protection.” In the United States, he told DW.
Essentially, your immune system is less efficient at tracking down and destroying omicron virus particles. This evasion is what has caused the massive spike in infections worldwide since the omicron was first discovered in southern Arica in November 2021.
Why delta is more lethal?
With all the omicron news lately, it’s easy to forget about the variants that came before – like delta. Delta is the most virulent type of coronavirus, leading to more severe symptoms and increased mortality among infected patients. UK statistics show that the risk of dying with an omicron is 67% lower than that of a delta infection.
Research has shown that deltas are particularly lethal due to mutations that occur on the spiny protein, which are protrusions on the surface of the virus. A new US-based study has found that two mutations cause an increase in the expression of the spike protein on the delta type of 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 cell-penetrating system is via a protein that is expressed on the surface of cells in your body, called ACE2. This protein serves as a door to your cells. It is usually locked and requires a key to open.
SARS-CoV-2 successfully tricks ACE2 into thinking it should be allowed into your cells. In essence, it is a replica of your house keys.
Biologically, the switches are the barbed proteins, which bind to ACE2. Once inside, the virus multiplies and spreads.
Corona virus enters human cells through its spiny proteins
For Delta, more spike proteins mean a greater ability to enter cells and multiply, which leads to higher amounts of coronavirus in the body.
Mallila, 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 the binding of the spike protein to an important class of antibodies [in the human body]. This causes higher rates of infection and worse symptoms.”
Future vaccines look to combat new variants
Coronavirus vaccines have been a huge success, reducing deaths and acute symptoms worldwide. However, new variants are likely to emerge in the coming years, and they can be much more transmissible and deadly.
Scientists are working hard to be one step ahead, to develop new coronavirus vaccines that train the immune system to deal with the new variants.
“There are about 220 candidate vaccines in clinical trials around the world,” Mallela said. “These updated vaccines will allow us to generate an immune response that is more appropriate to deal with the variables circulating at the time of vaccination.”
There is reason to be optimistic. For example, UK-based scientists recently demonstrated a promising new vaccine that better protects against novel variants of the coronavirus such as Omicron. The study authors used the new nanoparticle technology to create a vaccine that could be easily adapted to target future variants.
Editing: Carla Blecker