A study in PLOS Pathogens from the MRC-University of Glasgow Centre for Virus Research, United Kingdom, suggests that the Delta variant may be more successful at evading the protective response of vaccines.
The study, by Emma Thomson, Brian Willett, and colleagues, reports that mutations change the shape of the COVID-19 spike protein, preventing antibody recognition and enabling the virus to escape vaccine-induced immunity; however, the extent to which vaccine recipients are immune from the Delta variant is unknown.
To quantify the capacity of different variants (Alpha, Beta and Delta) to evade protective immune response in vaccines, the researchers analysed serum samples collected from healthy people who had received either the Pfizer or AstraZeneca vaccine: 156 people had received two doses and 50 people had received one dose.
They exposed SARS-CoV-2 proteins in a virus model system to sera from vaccinated people and observed the antibody response, measuring how effectively antibodies prevented each variant from infecting cells (virus neutralisation).
The researchers found that vaccines conferred protection from all COVID-19 variants but noted reduced antibody neutralisation of both the Beta and Delta variants. Across all vaccinated individuals, the Delta variant reduced the immune response in recipients of both the Pfizer and AstraZeneca vaccine 4.31 and 5.11-fold respectively. The study was not designed to measure vaccine efficacy directly, although it was in keeping with recent findings from Public Health England of slightly lower vaccine effectiveness against the Delta variant than previous variants. It also did not report on serological study of people who received the Moderna or Johnson & Johnson vaccines.
“While vaccines remain highly effective at preventing severe infection and death, ongoing monitoring of neutralisation against new variants alongside studies of vaccine effectiveness are indicated as the virus continues to evolve over time, especially in vulnerable groups,” said the authors. “Booster vaccines reduce the chance of being infected with currently circulating new variants. Newer updated vaccine designs are also likely to be required in time to prevent productive infection with newer variants of the virus.”
Study details
Reduced neutralisation of the Delta (B.1.617.2) SARS-CoV-2 variant of concern following vaccination
Chris Davis, Nicola Logan, Grace Tyson, Richard Orton, William Harvey, Jonathan Perkins, Guy Mollett, Rachel Blacow, Thomas Peacock, Wendy Barclay, Peter Cherepanov, Massimo Palmarini, Pablo Murcia, Arvind Patel, David Robertson, John Haughney, Emma Thomson, Brian Willett.
Published in PLOS Pathogens on 2 December 2021
Abstract
Vaccines are proving to be highly effective in controlling hospitalisation and deaths associated with SARS-CoV-2 infection but the emergence of viral variants with novel antigenic profiles threatens to diminish their efficacy. Assessment of the ability of sera from vaccine recipients to neutralise SARS-CoV-2 variants will inform the success of strategies for minimising COVID19 cases and the design of effective antigenic formulations.
Here, we examine the sensitivity of variants of concern (VOCs) representative of the B.1.617.1 and B.1.617.2 (first associated with infections in India) and B.1.351 (first associated with infection in South Africa) lineages of SARS-CoV-2 to neutralisation by sera from individuals vaccinated with the BNT162b2 (Pfizer/BioNTech) and ChAdOx1 (Oxford/AstraZeneca) vaccines. Across all vaccinated individuals, the spike glycoproteins from B.1.617.1 and B.1.617.2 conferred reductions in neutralisation of 4.31 and 5.11-fold respectively. The reduction seen with the B.1.617.2 lineage approached that conferred by the glycoprotein from B.1.351 (South African) variant (6.29-fold reduction) that is known to be associated with reduced vaccine efficacy.
Neutralising antibody titres elicited by vaccination with two doses of BNT162b2 were significantly higher than those elicited by vaccination with two doses of ChAdOx1. Fold decreases in the magnitude of neutralisation titre following two doses of BNT162b2, conferred reductions in titre of 7.77, 11.30 and 9.56-fold respectively to B.1.617.1, B.1.617.2 and B.1.351 pseudoviruses, the reduction in neutralisation of the delta variant B.1.617.2 surpassing that of B.1.351. Fold changes in those vaccinated with two doses of ChAdOx1 were 0.69, 4.01 and 1.48 respectively. The accumulation of mutations in these VOCs, and others, demonstrate the quantifiable risk of antigenic drift and subsequent reduction in vaccine efficacy.
Accordingly, booster vaccines based on updated variants are likely to be required over time to prevent productive infection. This study also suggests that two dose regimes of vaccine are required for maximal BNT162b2 and ChAdOx1-induced immunity.
See more from MedicalBrief archives:
Delta variant’s dominance in much of the world forces governments to change tack
Delta variant: Not just hyper-contagious but also multiplies more rapidly inside respiratory tract
Previous COVID prevents Delta infection better than Pfizer shot — Israel study
Boosters significantly strengthen immunity — Cov-Boost trial