Delhi’s April Covid surge was driven by Delta replacing Alpha variant: Paper
Delhi’s rapid surge of coronavirus disease (Covid-19) cases in April is linked to the Delta variant of concern B1.617.2 overtaking the earlier predominantly found Alpha variant B1.117, shows a yet-to-be peer-reviewed paper from the Institute of Genomics and Integrative Biology (IGIB).
The paper, which was uploaded to MedRxiv Thursday night, states that the B1.117 variant – which was initially reported from UK in December last year – was “minimal” in Delhi in the month of January, rapidly increasing to 20% in February, and 40% in March. Even this rapidly spreading variant of concern was, however, overtaken by April by the Delta variant first found in Maharashtra.
The proportion of the Delta variant increased from 5% in February to 10% in March, before overtaking the Alpha variant by April and accounting for 60% of the sequenced samples, according to the paper. This increase in the proportion of the Delta variant was paralleled by a large increase in the positivity rate.
The positivity rate – proportion of samples that return positive – in Delhi had jumped to over 36% by April third week, meaning one in every three samples being tested was found to have Covid-19.
Based on data from India and the UK, the researchers from IGIB estimate that the Delta variant is as much as 50% more transmissible than the Alpha variant, which is also manifold more transmissible that the wild-type Sars-Cov-2.
The researchers also found that the breakthrough infections – Covid-19 after immunisation – were disproportionately because of the Delta variant. They are yet to determine whether the variant also leads to increased case fatality ratio – proportion of deaths among positive cases.
“While much more remains to be done, three takeaways for now are: Delta (B.1.617.2) is more transmissible than Alpha (B.1.1.7), there seems to be greater immune escape and reinfection, and fully vaccinated breakthroughs were disproportionately due to Delta,” said Dr Anurag Agarwal, director, IGIB in a tweet.
An earlier study from the same institute found that it was causing more breakthrough infections in a tertiary care hospital. The researchers found that of the 33 healthcare workers who got the infection, almost half the infections were caused by B1.617 variant.
“The dominance of B.1.617 could be explained by prevalence of this lineage in community infection or simply reflect transmission among healthcare workers. The data nonetheless raises the possibility of a transmission advantage of B.1.617 in vaccinated individuals,” said the yet-to-be peer-reviewed article from mid-May.