Delta: a deep dive

From The Medical Republic, 2 August 2021:

At the start of this year, the covid situation in India was looking relatively good.

As the pandemic raged in other parts of the world, India was reporting around 10,000 new cases each day1 – nothing like the hundreds of thousands being diagnosed in the United States.

A new variant of the virus – labelled B.1.617 – had cropped up in October in India, but with infection rates dropping, it didn’t appear to be cause for concern.

Perhaps buoyed with a little too much confidence, India eased its public health restrictions. Festivals and political rallies went ahead with vast numbers of attendees2, but all the while, B.1.617 was quietly circulating. And as numbers of covid cases started to increase in the freely mingling population, the variant mutated.

On 5 February, a SARS-CoV-2 viral sample was taken from a young man in the Indian state of Tamil Nadu. Its genome was closely related to B.1.617, so it was given the designation of B.1.617.23. Then, that variant exploded, increasing from just 3% of cases in India in mid-March to 21% by the end of March and 96% two months after that.

On 11 May, the World Health Organisation designated viruses within the B.1.617 lineage as variants of concern, based on clear evidence that the variant was transmitting much more quickly and effectively than previous variants, and was spreading rapidly around the world.

Studies of its genome found mutations that could potential increase the ability of the spike protein to bind to the human ACE2 receptor – which enables SARS-CoV-2 to gain access to cells – as well as mutations that may have increased its transmissibility and even helped it avoid being neutralised by some antibodies.

The Delta variant, as it is now known, is now threatening many hard-won public health gains around the world, including the much-sought-after herd immunity. It has been likened to chicken pox in terms of its transmissibility, and emerging evidence suggests even the fully vaccinated transmit the Delta variant at the same rate as the unvaccinated. Read more.

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