According to a study published in the Nature Journal on Tuesday stated that the Delta variant of the SARS-CoV-2 virus, which has become the leading strain in India and many other countries that is most likely to spread through its ability to avoid neutralising antibodies and increased infection.
In late 2020 the Delta variant or B.1.617.2 was first observed in India. Since then, it’s spread around the world. Lab-based experiments and epidemiology of vaccine breakthrough infections were combined by the international team of researchers showing that the Delta variant is better at duplicating and spreading than other commonly-observed variants.
Professor Ravindra Gupta from the University of Cambridge in the UK, and one of the study’s senior authors said, “There’s also evidence that neutralising antibodies produced as a result of previous infection or vaccination are less effective at stopping this variant.”
“These factors are likely to possess contributed to the devastating epidemic wave in India during the first quarter of 2021, where as many as half the cases were individuals who had previously been infected with an earlier variant,” Gupta noted.
To examine how well the Delta variant was ready to evade the immune reaction , the team extracted serum from blood samples collected as a part of the COVID-19 cohort of the UK’s National Institute for Health Research (NIHR) BioResource. The samples came from individuals who had previously been infected with the coronavirus or who had been vaccinated with either the Oxford/AstraZeneca, referred to as Covishield in India, or Pfizer vaccines.
The serum contains antibodies raised in response to infection or vaccination. The team found that the Delta variant virus was 5.7-fold less sensitive to the sera from previously infected individuals, and therefore the maximum amount as eight-fold less sensitive to vaccine sera, compared with the Alpha variant.
In other words, it takes eight times as many antibodies from a vaccinated individual to dam the virus. The researchers also analysed over 100 infected healthcare workers at three Delhi hospitals, nearly all of whom had been vaccinated against SARS-CoV-2. They found the Delta variant to be transmitted between vaccinated staff to a greater extent than the Alpha variant.
“The Delta variant has spread widely to become the dominant variants worldwide because it’s faster to spread and better at infecting individuals than most other variants we’ve seen,” said Partha Rakshit from the National Centre for Disease Control, Delhi, and joint senior author of the study.
“It is additionally better at getting around existing immunity — either through previous exposure to the virus or to vaccination — though the danger of moderate to severe disease is reduced in such cases,” Rakshit said.
The spike proteins of the SARS-CoV-2 bind to ACE2, a protein receptor found on the surface of cells in our body. Both the spike protein and ACE2 are then cleaved, allowing genetic material from the virus to enter the host cell. The virus manipulates the host cell’s machinery to permit the virus to duplicate and spread.
Using 3D airway organoids — ‘mini-organs’ grown from cells from the airway, which mimic its behaviour — the team studied what happens when the virus reaches the tract . The researchers used both a live virus and a ‘pseudotyped virus’ – a man-made kind of the virus that mimicked key mutations on the Delta variant — and used this to infect the organoids. They found that the Delta variant was more efficient at breaking into the cells compared with other variants because it carried a bigger number of cleaved spikes on its surface.
Once inside the cells, the variant was also better ready to replicate. Both of those factors give the virus a variety advantage compared to other variants, helping explain why it’s become so dominant, consistent with the researchers.
Professor Anurag Agrawal from the CSIR Institute of Genomics and Integrative Biology, Delhi, India, joint senior author of the study, noted that infection of vaccinated healthcare workers with the Delta variant is a significant problem.
“Although they themselves may only experience mild COVID, they risk infecting individuals who have suboptimal immune responses to vaccination thanks to underlying health conditions — and these patients could then be in danger of severe disease,” Agrawal said.
“We urgently got to consider ways of boosting vaccine responses against variants among healthcare workers. It also suggests infection control measures will got to continue within the post-vaccine era,” he added.
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