Delta variant led to most post-vaccine infections in Delhi

Study from CSIR, NCDC scientists

June 04, 2021 09:50 pm | Updated November 30, 2021 06:26 pm IST - NEW DELHI

RT-PCR test of Covid 19 virus in progress at Adarsh Nagar in North Delhi

RT-PCR test of Covid 19 virus in progress at Adarsh Nagar in North Delhi

Variant Delta (B.1.617.2), the most pervasive variant of the coronavirus in India, constituted nearly three in four breakthrough infections in Delhi, according to a research study by scientists in Delhi. The variant was also characterised by high transmissibility, an accelerated surge in infections and, the scientists say, “...prior infections, high seropositivity and partial vaccination were insufficient impediments to its spread.”

Breakthrough infections are instances of people testing positive for the virus after getting vaccinated.


The study is yet to be peer-reviewed and appears as a pre-print and was authored 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.

In 27 instances of breakthrough infections analysed, the scientists found that two lineages dominated. B.1.617.1 (Kappa) comprised 8%, Delta was 76% and the remaining linked to variants that belonged to broader “B.1 lineages”. However international variant Alpha, that in previous studies has been associated with a spike in cases in Delhi in February and March was absent in vaccination breakthrough-cases analysed.

The study also reports a new mutation in Delta called T478K that the scientists believe has a role to play in allowing the coronavirus to better infiltrate human cells.

“Our data indicates B.1.617.2 shows high transmissibility and surges without any increase in the Case Fatality Ratio (CFR). We estimate the transmissibility to be as much as 50% greater than B.1.1.7. 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,” they note in their study.

Anurag Agrawal, Director, CSIR-IGIB and among the authors of the paper said that while the variant was extremely transmissible, there was no single super spreader event that contributed to the rise of the Delta variant in Delhi. Previous studies had shown that the farmer protests and religious gatherings had contributed to amplifying the Alpha variant in North India. The latter variant has now been outcompeted by the Delta.


“We should be doing more studies on the vaccine effectiveness in India against various strains. We must also assess the risk to various populations, by age, to decide on the dosage of vaccine.” Dr Agrawal said.

Though India is seeing a decline overall in the case trajectory, the Delta variant has been responsible for a surge of cases in the United Kingdom, as well as shown to reduce the efficacy of vaccines.

A study in the medical journal Lancet, published on Thursday, comparing antibodies generated due to vaccines in those afflicted by varying strains in the United Kingdom, found that they were nearly six-fold reduced against B.1.617.2 relative to the original Wuhan-strain of the virus. By comparison antibody levels were reduced just 2.6 times against Alpha when compared to the Wuhan strain.

Studies by the ICMR have also shown that fewer antibodies were expressed in those vaccinated with Covaxin and Covishield when their blood serum was tested against the Delta strain in labs.

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