Highlights:

  • The B.1.617 variant and its lineage B.1.617.2 were primarily responsible for the surge in Covid-19 cases with high transmissibility
  • The rise in prevalence of the Delta variant was first detected in India in April
  • The study further clarifies that increase in Covid-19 deaths was associated with the collapse in healthcare system and not variant
  • It was the Delta variant that led to several infections even among vaccinated individuals

A study carried out by the scientists of INSACOG, which is a consortium of labs undertaking genome sequencing in India and the National Centre for Disease Control (NCDC), has revealed that despite people of Delhi have seropositivity of over 56 percent, they did not get much protection against the Delta variant after it took over the national capital March 2021 onwards. This test was done to look for the reasons behind the second wave that swept North India.

About the sharp spike in Delhi, the study says, “After touching the high of almost 9,000 cases daily and a positivity rate of about 15 percent during the third wave in November 2020, new cases steadily declined, with only 1 percent positivity between December 2020 and March 2021. This reversed and started increasing from the third week of March 2021, shooting to 30 percent by end of April, with almost 30,000 cases being reported per day”.

The study also adds that the B.1.617 variant and its descent B.1.617.2 were mainly responsible for the surge in Covid cases with high transmissibility of 50 percent more than the UK or Alpha variant (B.1.1.7). The B.1.617.2 Alpha variant, first detected in the UK, was seen in an increasing number of cases between February and March. The B.1.617 Delta variant, which was detected in India, later overtook in April.

The study mentioned, “The CFR (case fatality rate) values, which were constant from December till February 2021, witnessed a significant decrease with a simultaneous increase from March. This may be due to the sudden decrease of B.1.1.7 in the Delhi region, which reportedly causes high CFR. The case fatality rate was rising again towards the end of this period. Since CFR may be due to an amalgamation of multiple factors, including the short-term collapse of the healthcare system, there is currently no clear evidence linking B.1.617.2 to the change in CFR”.

The study also clarified that the increase in Covid-19 deaths was due to the collapse in the healthcare system and not the variant. It also showed that the Delta variant led to several infections even among vaccinated individuals.

The authors advised, “While immune escape seems less for B.1.617.2 compared to B.1.351 or P.1 overall, we note that B.1.617.2 is capable of creating very fast-rising outbreaks with vaccination breakthroughs. We would re-emphasize that prior infections, high seropositivity, and partial vaccination are insufficient impediments to its spread, as seen in Delhi, and strong public health response will be needed globally for its containment”.

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