A recent study conducted by scientists of INSACOG and the National Centre for Disease Control (NCDC) has shown that despite having a high seropositivity rate of 56 per cent, people of Delhi got little protection against the Delta variant of the coronavirus that took over the national capital in March 2021 causing an unprecedented rise in cases. The study was focused on determining the reason behind the second wave of the COVID-19 pandemic which swept much of North India.
What caused COVID-19 second wave in India?
Explaining the sharp spike in Delhi during March 2021, the study noted, "After touching the high of almost 9,000 cases daily and a positivity rate of about 15 per cent during the third wave in November 2020, new cases steadily declined, with only 1 per cent positivity between December 2020 and March 2021. This reversed and started increasing from the third week of March 2021, shooting to 30 per cent by end of April, with almost 30,000 cases being reported per day."
The study stated that the B.1.617 variant (Delta) and its lineage B.1.617.2 were primarily responsible for the surge in COVID-19 cases. These had a 50 per cent higher transmissibility rate than the B.1.1.7 variant (Alpha) of the virus. The study added that B.1.617.2 variant was discovered in an increasing number of cases during February-March in the country. This variant was later overtaken by the Delta variant in April 2021. The rise in presence of the Delta variant in the country corresponded with the surge in the overall positivity rate.
Surge in COVID-19 deaths caused by failure of the healthcare system
The study has showcased that the Alpha variant of the coronavirus had a higher case fatality ratio compared to the Delta variant. Hence, the study clarified that the surge in COVID-19 related deaths during the second wave of the outbreak was caused by the failure of the healthcare system rather than a specific variant of the virus.
Delta variant caused infection in vaccinated people
The study has stated that the Delta variant had even caused COVID-19 infections among vaccinated people. "B.1.617.2 was over-represented and B.1.1.7 was not even detected in vaccination breakthroughs, suggesting higher breakthrough risk of B.1.617.2 compared to B.1.1.7," noted the study.
Effects on other states
The study showed that outbreak in Kerala, Maharashtra and Punjab preceded the April 2021 outbreak in the national capital. No variant of concern was identified in Kerala in January 2021.
The outbreak in Maharashtra has been related to B.1.617.1 and in Punjab to B.1.1.7. These variants have been found to be phylogenetically related. There is a strong evolutionary connection between Delhi and Punjab for B.1.1.7 and between Delhi and Maharashtra for B.1.617 lineages, according to the study.
Study raises some concerns
The study has determined that the viral load of the Delta variant is much higher than the Alpha variant. The same case is for vaccination breakthrough rate, according to data from India and the UK.
The authors have 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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