Explained: The Delta Variant Of COVID-19 Virus That Caused 75 Per Cent Of Post-Vaccine Infections In Delhi

A study by scientists at the CSIR-Institute of Genomics and Integrative Biology (CSIR-IGIB) and the National Centre of Disease Control — two key labs of the Indian Sars Cov-2 Genomic Consortium (INSACOG) that tracks the emergence of key variants of the coronavirus — claims that novel Coronavirus variant ‘Delta’ (B.1.617.2) caused three out of four ‘breakthrough’ infections in Delhi.

Breakthrough infections refer to the instances of people who are already vaccinated testing positive for the COVID-19. The study is yet to be peer-reviewed and appears as a pre-print, reports The Hindu.

B.1.617 is the name of a double variant of COVID-19 that was, for the first time, detected in Maharashtra, India (It was erroneously referred to as the ‘Indian variant’ by the press). It carries two mutations, E484Q and L452R. While both are separately found in many other coronavirus variants, they were observed together for the first time in India.

Together, the two mutations make the virus more infectious, and help it evade antibodies.

Its variant Delta, or B.1.617.2, is reportedly the most pervasive variant of the Coronavirus in India and is characterised by high transmissibility and an accelerated surge in infections.

The scientists note that “...prior infections, high seropositivity and partial vaccination were insufficient impediments to its spread.”

The variant reportedly has 12 mutations in its spike protein compared to the SARS-CoV-2 which was first reported in Wuhan, China.

The L452R and T478K mutations characterise the variant, and scientists have found more ACE2 enzymes aiding the entry of virus into human body.

The study notes that B.1.617.2 shows high transmissibility (as much as 50 per cent greater than B.1.1.7 — what is popularly known as the ‘UK variant’ in the press) and surges, but without any increase in the Case Fatality Ratio (CFR).

It also says that the viral load of B.1.617.2 appears to be higher than B.1.1.7 and based on data from India and UK, so does vaccination break-through rate.

“B.1.617.2 is capable of creating very fast rising outbreaks with vaccination breakthroughs,” the study says.

Against Delta variant (B.1.617.2), a study by Public Heath England (PHE) found the Astra-Zeneca and Pfizer vaccines to be 33 per cent effective, as opposed to around 50 per cent effective against B.1.1.7.

The PHE further found that 61 per cent of cases in UK are caused by Delta, in the week beginning 17 May, by the analysis of genome sequencing data.

The scientists in India analysed 27 instances of breakthrough infections and found two lineages primarily responsible — B.1.617.1 (Kappa) comprised 8 per cent of the infections while Delta was responsible for 76 per cent of them. The remaining cases were linked to variants belonging to broader “B.1 lineages”.

The international variant Alpha, that previous studies found associated with a spike in cases in Delhi in February and March, was absent in the analysed cases. It has now been overtaken by the Delta variant.

WHO, which has given the variant its label ‘Delta’, has categorised it as a variant of concern (VOC).

Also read: Here’s All You Need To Know About COVID-19 Strains