COVID-19 Delta Variant Able to Evade Vaccine-Induced Immunity

Tom Broder

December 03, 2021

The emergence of novel COVID-19 variants such as the Delta variant, currently dominant in the UK, may reduce the efficacy of vaccines developed using the original virus.

study published this week in PLOS Pathogens , by researchers at the MRC-University of Glasgow Centre for Virus Research, found that the Delta variant reduced antibody immune response in serum samples from vaccinated volunteers.

The Glasgow study compared the Delta variant with both the original Wuhan strain of the virus and the Beta variant first detected in South Africa in 2020. The Beta variant is already known to be associated with reduced vaccine efficacy.

The Delta variant reduced neutralising antibody activity 5.11-fold in comparison with the Wuhan strain, a level approaching that observed for the Beta variant, suggesting a similar reduction in vaccine effectiveness.

Emma Thomson, professor of infectious diseases at the MRC-Glasgow Centre and a co-author of the study, told Medscape UK: “This study provides further confirmation that the Delta variant may reduce the effectiveness of current vaccines due to a reduction in antibody neutralisation.”

The authors emphasise that vaccines continue to prove highly effective in controlling hospitalisations and deaths associated with COVID-19.

But in light of this study, as well as the recent emergence of the heavily mutated Omicron variant, they warn: “Booster vaccines based on updated variants are likely to be required over time to prevent productive infection.”

Variants of Concern

As the SARS-CoV-2 virus has evolved over time, new viral variants have emerged that incorporate mutations in the virus ‘spike protein’ - the main target of neutralising antibodies. Mutations change the shape of the spike protein, preventing antibody recognition and helping the virus evade vaccine-induced immunity.

To explore the extent to which vaccine-induced antibodies protect against Delta, the Glasgow study collected serum samples from 156 healthy adult volunteers taking part in the COVID-19 Deployed Vaccine Study (DOVE). Participants had all received one or two doses of the Pfizer/BioNTech or Oxford/AstraZeneca vaccines.

The researchers exposed the serum samples to Delta and Beta variant pseudovirus proteins, as well as those from the original Wuhan-Hu-1 strain of the virus, and observed the antibody response. Across all vaccinated individuals in the study, the Delta variant reduced neutralising antibody titres 5.11-fold and the Beta variant 6.29-fold.

Among participants who received two doses of the Pfizer-BioNTech vaccine, providing a better baseline response, the study observed an 11.30-fold reduction in antibody titres for the Delta variant and 9.56-fold reduction for the Beta variant.

“Antibody neutralisation may provide an early indication of the future efficacy of vaccines against new variants, including Omicron” Professor Thomson told Medscape UK.

“Sequencing studies and neutralisation studies provide early warning signals about the likely impact on vaccine effectiveness before a variant becomes dominant in the population. We are currently running similar neutralisation assays to understand the Omicron variant and expect the initial results in the next 2 to 3 weeks.” 

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