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Delta Variant: Antibodies Do Not Match

People previously infected with SARS-CoV-2, the virus that causes COVID-19, are more likely to be reinfected with Delta variant—new study reports.

In the new study published July 8 in the journal Nature, the lead scientists from Institut Pasteur, Franch investigated the sensitivity of the Delta variant to monoclonal antibodies, which are used to prevent disease severity, and to neutralize antibodies in the blood of people who are either previously infected with SARS-CoV-2 or vaccinated. They observed that the Delta variant potentially modifies virus binding to the receptor and allows partial escape from the immune response (Planas et al., 2021).

Delta Variant and its Transmissibility

The Delta variant scientists first identified in India in October 2020 (Yadav et al., 2021). The variant was later found in the UK and thought to spread to many other countries, including France, Russia, and Portugal.

Epidemiological studies further show that the Delta variant is approximately 60% more transmissible than the Alpha variant (Public Health England 2021). In recent weeks, the number of delta-diagnosed cases has risen in many countries, including the UK and France. From June 23 to June 30, 2021, over 135,000 individuals were tested positive in the UK. Of the positive cases, 70-90% of the sequenced virus were among delta variants. In France, during the last week of June, 20% of new cases in France were delta variants compared to the 9% of the previous week.

delta variant

The primary characteristics scientists found are its increased disease severity, causing detection failure, and reduced generation of neutralizing antibodies.

The variant’s detail virulent characteristics are yet to be investigated. However, studies show that its spike protein has several levels of mutation in the N-terminal end and receptor binding domain that make the variant immune evasion potential. At least nine mutations have been found in the N-terminal domain.

Considering its high transmissibility and increased disease-causing severity, leading health organizations, including WHO, CDC has already designated the variant as a ‘Variant of Concern.’

Immune Response: Delta Variant vs. Other Variants

In collaboration with Hôpital Européen Georges Pompidou, Orléans Regional Hospital, and Strasbourg University Hospital, the Institut Pasteur scientists compared the sensitivity with that of the virus previously circulating in France known as Alpha (the UK variant) and Beta (the South African variant), and the antibodies generated after a single and double dose of Pfizer or AstraZeneca vaccines.

In the new study, the French scientists collected SARS-CoV-2 variant Delta from a nasal sample of an individual who developed COVID-19 a few days after returning from India in April 2021.

While examining its sensitivity to various antibodies, the scientists found that the Delta variant was resistant to neutralization by anti-NTD and anti-RBD mAbs, including Bamlanivimab, which were impaired in binding the spike. Convalescent plasma collected from patients up to 12 months post symptoms was fourfold less potent against variant Delta than variant Alpha (B.1.1.7).

The researchers found that Pfizer or AstraZeneca vaccine antibodies generated after the first dose barely inhibited the delta variant, as the generated antibodies provided only 10 percent protection against the variant. The second dose of vaccine generated neutralizing antibodies in 95% of vaccinated cases. However, the antibodies were three to fivefold less potent against Delta than Alpha, the variant first identified in the UK.

The scientists also showed that a few antibodies, including Bamlanivimab, are no longer active against the variant, but other Etesevimab, Casirivimab, and Imdevimab were functional.

Author’s Opinion

“This collaborative multidisciplinary effort involved the Institut Pasteur’s virologists and specialists in the analysis of viral evolution and protein structure.”, said Olivier Schwartz, co-last author of the study and Head of the Virus and Immunity Unit (Institut Pasteur/CNRS).

“We demonstrated that this variant, which spreads more rapidly, has acquired partial resistance to antibodies,” said Olivier Schwartz.

“The blood patients previously infected with COVID-19, collected up to 12 months after they developed symptoms, and of individuals who had received two doses of the Pfizer or AstraZeneca vaccine are still neutralizing but are three to six-fold less potent again. Furthermore, the sera of individuals vaccinated with a single dose of the Pfizer or AstraZeneca vaccine are relatively or entirely ineffective against the Delta variant,” continues Olivier Schwartz.

The scientists concluded that the spike protein’s mutations potentially change the binding ability to the receptor protein and allow partial escape from the immune response. Ongoing studies are now focusing on understanding why this variant is more transmissible than others.

Related Publications

Public Health England (2021), “SARS-CoV-2 variants of concern and variants under investigation in England.” technical briefing 12.
Planas, D., D. Veyer et al. (2021), “Reduced sensitivity of SARS-CoV-2 variant Delta to antibody neutralization.” Nature. 10.1038/s41586-021-03777-9.
Yadav, P. D., G. N. Sapkal, et al. (2021) “Neutralization of variant under investigation B.1.617 with sera of BBV152 vaccinees.” Clinical Infectious Diseases. 10.1093/cid/ciab411.  

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