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World How the coronavirus Delta variant rampaged through India before spreading across the globe

23:25  08 june  2021
23:25  08 june  2021 Source:   abc.net.au

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For a bustling, crowded, mega-city, the Indian capital Delhi was a relatively calm place in February and March.

Daily confirmed infections were in the low hundreds and serological surveys, which detect COVID-19 antibodies in the blood, suggested more than half the city's population had been infected after overcoming three surges.

The city was, according to Delhi's Health Minister, "inching" towards herd immunity, but disclaimers urging the public to remain vigilant were drowned in a sea of complacency.

India's vaccine rollout had begun in a methodical, albeit slow, fashion with a commitment to only target 300 million of the country's 1.3 billion people, focusing on elderly residents and frontline workers over a six-month period.

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India was falling short of its relatively modest targets, but there seemed to be little concern. Health Minister Harsh Vardhan declared India was "in the endgame" of the pandemic.

It was as if time was on India's side.

But health experts, such as Joyeeta Basu, who runs the Doctors Hub clinic just outside Delhi, knew the virus did not give up.

"We have a small, tiny window of opportunity," Dr Basu warned the ABC in February.

"If there's even a single slip and the variants start, then heaven help us."

Experts confounded by pace of catastrophic surge

The calamity that followed in the weeks after that interview is well known.

Mask wearing and social distancing declined, and large public gatherings, including political rallies and religious festivals, were allowed to continue virtually unabated, creating a prime environment for the virus to spread so quickly it was better described as a tsunami than a wave.

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It took just a few weeks for an "uptick" in cases to surge past the country's previous national record of 100,000 daily infections. A month later, it had surpassed 400,000 daily infections and 4,000 deaths.

The sheer overwhelming of the country's testing regime, hospitals, and crematoriums led experts to conclude such figures were a gross undercount.

Entire households were infected at a much greater rate than previous surges, even if infected family members had been isolating.

Authorities advocated for people to wear two masks, even going so far as to promote wearing masks when inside the home and keeping windows and doors open to maximise ventilation.

Now, on the other side of India's massive surge, Dr Basu wishes her predictions were wrong.

"We had so many virologists and epidemiologists who had been shouting through the roof," she said.

"[The virus] just took advantage of the whole Indian scenario.

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"The consequences are here for you to see."

While poor behaviour was blamed for igniting and fuelling the second surge, it did not adequately explain the rapid speed of the infection.

The missing piece had to be the variants, experts theorised, but a lack of data made it hard to get a complete picture.

"If I put all of those factors — the public disregard for COVID-appropriate behaviour, the waning immunity potential for reinfection, large gatherings happening — all of that together probably cannot explain the surge that we saw," epidemiologist Bhramar Mukherjee, from the University of Michigan, told the ABC in May.

"The proportion of cluster infections increased. The variant is so transmissible that the families could not really escape."

From India to the world: Delta rises to viral dominance

India first revealed what it called the "double mutant" variant in late March.

It has since been split into two variants: Delta, or B.1.617.2, and Kappa, or B.1.617.1.

While less is known about Kappa, Delta has since spread to dozens of countries around the world, and is renowned to be more infectious than previous versions.

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They have created considerable concern for Victorian authorities responding to the state's latest outbreak.

But in March, Indian authorities were much more concerned about the UK variant, now known as Alpha, as it had been linked to an uptick in cases in places like Punjab while they claimed the "double mutant" strain had not.

Three months later, researchers have finally been able to demonstrate Delta was indeed responsible for the aggression of the second, catastrophic surge, notably in the country's north.

A joint study by India's National Centre for Disease Control and the CSIR Institute of Genomics and Integrative Biology, which is yet to be peer reviewed, found the Delta variant made up the lion's share of 878 test samples from New Delhi in April.

Just a month earlier, in March, the Alpha variant had been dominant.

The fact the Delta variant quickly displaced Alpha in Delhi and nearby regions suggested to the experts it was considerably more infectious.

It was up to 50 per cent more infectious than the Alpha strain, researchers concluded, and had a stronger ability to break through COVID-19 immunity resulting from past infection or vaccination.

Senior co-author Anurag Agrawal told the ABC it was the first study in India to link a variant to a major outbreak.

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"If there was no Delta [variant] and only the Alpha variant came into India, would we have had an outbreak like this? I don't think so," Dr Agrawal said.

The report noted infections among those who had been fully vaccinated were "usually mild", and the variant itself did not lead to a higher rate of death.

But India was greatly exposed at the onset of the second surge, with less than 2 per cent of the population fully vaccinated.

The high rate of antibodies from previous infections was simply not enough to repel the Delta variant, Dr Agrawal said.

"A city with 50-plus [percentage of] sero-positivity would have at least served as an impediment to the rapid outbreak of disease and the outbreak would have not been as bad," he said.

"You would have expected Delhi to do better. It's a working hypothesis."

The Delta variant has now also become the dominant variant in the UK after outperforming the Alpha variant.

In both India and the UK, the Kappa variant has not made nearly as much of a mark as its Delta relative, demonstrating it is considerably less infectious, Dr Agrawal said.

"Ultimately, the one that gets attention is the one that creates the outbreak," he said.

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Healthcare workers fighting India's second surge reported more varied and severe symptoms among COVID-19 patients, particularly among the younger population.

In previous surges, only about one in 10 patients suffered from depleting oxygen levels, whereas in this surge it was experienced by every second patient, Dr Basu said.

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Oxygen levels in patients also started to drop sooner than before.

The strain on medical oxygen supplies was so chronic that major hospitals across the country ran out, leading to even more deaths.

"Definitely the variants were responsible," she said.

"What upsets me the most is it could have been prevented and at least 50 per cent of the deaths could have been prevented if we had enough oxygen."

Not only did India's testing regime fail to keep pace with the rate of infection, leading to positivity rates in Delhi of up to 38 per cent, but the country also had a poor record for genomic sequencing.

By the end of April, less than 1 per cent of India's positive COVID-19 samples had been sent for genomic sequencing, compared to 60 per cent in Australia and 9 per cent in the UK, according to not-for-profit organisation GISAID, which provides open-source COVID-19 data.

Dr Basu said a lack of reliable data meant there was still much to learn about the Delta variant.

"Research in our country needs to be more advanced," she said.

"If you look at what the UK is doing, it's just brilliant."

Dr Agrawal said despite the concerns surrounding Delta's transmissibility, the basic preventative measures to stop the spread of coronavirus remained the most effective way to prevent infections and outbreaks.

"We have seen once the lockdown in Delhi was imposed, the infections came down," he said.

"If everyone was wearing masks, the number of infections would go down drastically.

"Clearly, standard public health measures work."

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