The coronavirus SARS-CoV-2 is quite versatile, with a large number of variants and subvariants. The omicron variant alone has more than 130 sublineages.

In Europe, the omicron subvariants BA.4 and BA.5 are currently on the rise. Why are they spreading so fast, despite the fact that 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 is believed to change how the virus functions. Typically, these variants have increased infection rates and increased disease severity," Krishna Mallela, professor in the department of pharmaceutical sciences at the University of Colorado in the US, told DW.

Now scientists are beginning to understand why specific mutations cause variants to be 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 off.

A recent study from the US showed that omicron is more infectious because it can better evade our immune system.

After vaccination or a prior infection, antibodies circulate in your body and hunt for viruses. They detect coronavirus via its spike protein, which then signals for the virus to be neutralized.

The study shows that the mutations in omicron subvariants BA.1 and BA.2 change the structure of the spike protein.

"The mutations are at the spots where antibodies bind to the spike protein. The mutations cause a different binding surface, which is less recognized by the antibodies. This leads to the evasion of antibody protection," Kamal Singh, an immunologist from University of Missouri in the US, told DW.

Essentially, your immune system is less good at hunting down and destroying omicron virus particles. This evasiveness is what caused the huge rise in infections around the world since omicron was first identified in South Arica in November 2021.

Why is delta more deadly?

With all the omicron news lately, it's easy to forget the variants that came before — like delta. Delta is the most virulent coronavirus variant, leading to more severe symptoms and increased mortality among infected patients. UK statistics show that risk of death with omicron is 67% lower than delta infection.

Research has shown that delta is particularly deadly because of mutations on the spike protein, protuberances on the surface of the virus. A new US-based study found that two mutations cause increased expression of the spike protein on the delta variant of the virus.

That's important because SARS-CoV-2 is like a thief trying to sneak into your house, or rather your cells — and it does this 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 door into your cells. Normally it's closed and requires a key to open it.

SARS-CoV-2 has managed to trick ACE2 into thinking it should be let into your cells. In essence, it's duplicated the keys to your house.

In biological terms, the keys are the spike proteins, which bind to ACE2. Once inside, the virus then replicates and spreads.

For delta, more spike proteins mean greater ability to enter cells and reproduce, leading to higher quantities of coronavirus in the body.

Mallela, the study's lead author, explained how the mutations also affects the immune system's ability to neutralize the virus.

"Our study found delta reduces the spike protein binding to an important class of antibodies [in the human body]. This causes higher infectivity rates and worse symptoms," he said.

Future vaccines look to combat new variants

Coronavirus vaccines have been hugely successful, reducing mortality and severe symptoms worldwide. However, new variants are likely to appear in the coming years, and they could be more transmissible and deadly.

Scientists are working hard to be one step ahead, 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," said Mallela. "These updated vaccines will allow us to generate an immune response that is better suited to tackle the variants that are in circulation at the time of vaccinating."

And there's reason to be optimistic. For example, UK-based scientists recently showcased a promising new vaccine that better protects against newer coronavirus variants like omicron. The study authors used new nanoparticle technology to create a vaccine that can easily be adapted to target future variants.