French Study Confirms the Effectiveness of Vaccination on the Delta Variant

The effectiveness of 2-dose vaccination on the Delta variant has been confirmed in a new French study. The results of this study are consistent with hospitalization data from Britain and Israel.

Coronavirus Vaccine

Coronavirus Vaccine

The SARS-CoV-2 variant B.1.617, or “Delta variant” (or “Indian variant”), was identified in India in the fall of 2020 and has since become widespread in that country and the United Kingdom. The Delta variant has since spread to many countries, and of course to the US.

This variant is 60% more contagious than the Alpha variant and was be the cause of the epidemic wave in Britain in the fall and in the rest of Europe in early 2021.

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A new French study, published in Nature, confirms that the Delta variant is less susceptible to antibodies developed after infection or a single dose of vaccination. This study confirms previous studies that suggested that the Delta variant could partially escape the immune system, although to a lesser degree than the Beta variant, which first appeared in South Africa.

An analysis of target regions on the Spike protein

The Indian variant series includes three main subtypes (B1.617.1, B.1.617.2, and B.1.617.3), which exhibit different mutations on the Spike protein, and it is these mutations that may increase the potential for immune evasion of the variants.

The French researchers tested the ability of antibodies, produced by natural infection and after one or two doses of the different vaccines, to neutralize the Alpha, Beta, and Delta variants, compared to a reference variant similar to the original version of the virus.

Lower sensitivity to natural antibodies and vaccines

The researchers first examined blood samples from 103 people previously infected with the other coronavirus variants. In this analysis, the Delta variant (Indian variant) was much less susceptible than the Alpha variant (English variant) to blood samples from these recovering, unvaccinated individuals. One dose of vaccine significantly increased variant susceptibility, suggesting that people recovering from Covid-19 need to be vaccinated with one dose to protect against some variants.

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The team then analyzed samples from 59 people after they received either an initial dose or 2 doses of the AstraZeneca or Pfizer-BioNTech vaccines. After a single dose, only 10% of the blood samples were able to neutralize the Delta (Indian) and Beta (South African) variants in a test tube. But the second dose increased this number to 95%.

There was not much difference in the antibody levels obtained with the two vaccines, but titers were 3 to 5 times less effective against the Delta variant (Indian variant) than against the Alpha variant (English variant). Thus, the spread of the Delta variant (Indian variant) is accompanied by at least partial antibody escape directed against the non-RBD and RBD-Spike epitopes.

Reduced sensitivity to monoclonal antibodies

The researchers also isolated a Delta infectious strain from a traveler returning from India and examined its sensitivity to the monoclonal antibodies used as a treatment in Covid-19. They also tested this variant against antibodies present in the sera of individuals recovering from Covid-19, and in comparison with other strains.
Thus, the Delta variant would be more resistant to neutralization by certain anti-NTD and anti-RBD monoclonal antibodies, including Bamlanivimab, since these antibodies have difficulty binding to the Spike protein. Sera from convalescent patients collected up to 12 months after symptoms were 4 times less potent against the Delta variant compared to the Alpha variant.

Consistency with field data

Field data from Israel and the United Kingdom, the countries most advanced in vaccination, largely confirm these findings. Reassuringly, they indicate that a single dose of vaccine would nevertheless be sufficient to prevent hospitalizations or deaths due to SARS-CoV-2.

The increase in infections observed in Israel in vaccinated individuals is mainly due to asymptomatic individuals who are merely carriers of the virus. The majority of these people would be overdiagnosed due to the very active policy of testing and tracking patients in this country.

In fact, hospitalization is not increasing in Israel and is increasing very slowly in the UK, mainly in unvaccinated individuals. Thus, vaccination can break the link between the spread of the Indian variant and hospitalizations, possibly after the first dose and even more so after 2 doses, according to the UK government.

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Possibly a 3rd dose

Currently, there is much debate about the need for a third dose in those at risk, about 30% of whom do not develop an adequate immune response.

However, this 3rd dose would not be necessary for vaccinated and healthy people, according to the FDA and the U.S. CDC, although Pfizer and BioNTech have simultaneously filed for approval in this direction.

Therefore, the priority in the US remains the accelerated vaccination of those who are not vaccinated, especially if they are over 45 years old and suffer from comorbidities such as diabetes and cancer.

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References

Reduced sensitivity of SARS-CoV-2 variant Delta to antibody neutralization

Vaccines highly effective against hospitalisation from Delta variant

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