DNA Explainer: Why the Delta variant of COVID-19 spread like wildfire across the world

As the Delta variant of the COVID-19 continues to create havoc, scientists are trying to understand the basis for the transmission. What has been found alarming is that this variant doesn't just spread faster than the original Wuhan strain, but is more transmissible and there is reduced vaccine effectiveness against it.

This means that even a fully vaccinated person is at risk of catching an infection from this variant of COVID-19. The Delta variant is fast becoming the dominant COVID-19 strain in many countries.

Many studies also found that the high infectiousness during the pre-symptomatic phase in patients is among the main reasons leading to the rapid spread of the virus, meaning the people are in danger of spreading the virus even before they come to know that they are infected. Research has proved that the Delta variant (B.1.617.2) is at least 40% more transmissible than the Alpha variant first identified in the UK in late 2020. 

As per the US Centers for Disease Control and Prevention (CDC), the Delta variant is more transmissible than the MERS, SARS, Ebola, the common cold, the seasonal flu, and smallpox viruses and is as contagious as chickenpox.

What makes Delta variant more infectious?

The original Wuhan strain has an R-value of 2-3 but Delta's R-value is about 5-6 (some researchers say this figure is even higher). Due to this, someone who is infected with the Delta variant is likely to infect at least twice as many people as the original Wuhan strain. R-factor or R-value is a way of rating a disease's ability to spread and indicates how many people can get infected from a single COVID-positive person.

A study found that 74% of infections with Delta took place during the pre-symptomatic phase, which means people spread the virus before knowing they are infected.  

Another recent research suggests that a key amino acid mutation may be behind the ferocious infectivity of the Delta variant. A team of researchers led by virologist Pei-Yong Shi found a key mutation that alters a single amino acid in the SARS-CoV-2 spike protein. The change is called P681R and transforms a proline residue into an arginine, as per a report on the study published in Nature journal.

The study states that the P681R mutation holds the key to the Delta variant's high infectivity and rapid transmission. The change occurs in the spike protein's furin cleavage site. In order to penetrate cells, the SARS-CoV-2 spike protein must be cut twice by host proteins.

The furin cleavage site in COVID-19 is significant because it means that the host enzymes, including furin, can make the first cut. After this, newly formed viral particles emerge from an infected cell which can infect the host cells more efficiently.

The study states that in the case of the Delta variant, the mutation that alters the furin cleavage has had a profound effect.

Previous studies found that other key mutations in the Delta variant such as L452R and D6146 allow the virus to attach more firmly to receptor cells and escape immunity more easily.

(With Inputs from Nature journal)