Delta variant appears capable of avoiding protection of Pfizer COVID vaccine

GLASGOW, Scotland — COVID-19’s seemingly never-ending list of variants continue to prolong the global pandemic. While the coronavirus vaccines have proven very effective at protecting the public, every new strain of the virus threatens to weaken that shield. With that in mind, a new study finds the highly infectious Delta variant appears to be capable of avoiding the protective response of the Pfizer or Astra Zeneca vaccines.

Researchers from the United Kingdom and MRC-University of Glasgow Centre for Virus Research say mutations in the SARS-CoV-2 virus change the shape of the spike protein — which the virus uses to hijack cells and reproduce in the human body. These changes make it harder for antibodies to recognize COVID-19 and block its spikes from attacking cells. While previous studies have started examining how this weakens protection from the Alpha and Beta variants, the team says it’s unclear how well vaccines protect against the newer Delta variant.

Study authors examined blood samples from over 200 healthy individuals who received the Pfizer or Astra Zeneca COVID vaccines. Out of this group, 156 received both doses of the vaccine while 50 only had one dose at the time of the study.

Scientists exposed these vaccinated blood samples to the Alpha, Beta, and Delta strains of the SARS-CoV-2 virus. From there, they measured the antibody response to each variant and how well COVID antibodies prevented the illness from infecting healthy cells — a process called virus neutralization.

Delta may significantly increase breakthrough risk

The study finds both brands of the vaccine protected patients against all three variants of COVID-19 however, virus neutralization dropped when antibodies encountered the Beta and Delta variants. Moreover, the Delta variant reduced the immune response of the Pfizer shot by over four times. Delta also reduced the protection of the Astra Zeneca vaccine by more than five times.

Study authors note that their tests did not measure the effectiveness of either the Moderna or Johnson & Johnson vaccines. Previous studies have found that the Moderna vaccine has produced the highest levels of protection against COVID-19 and its variants. Meanwhile, protection from the Johnson & Johnson shot has declined the most as new mutations emerge.

“While vaccines remain highly effective at preventing severe infection and death, ongoing monitoring of neutralization against new variants alongside studies of vaccine effectiveness are indicated as the virus continues to evolve over time, especially in vulnerable groups. 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,” the study authors say in a media release.

The study is published in the journal PLOS Pathogens.

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About the Author

Chris Melore

Chris Melore has been a writer, researcher, editor, and producer in the New York-area since 2006. He won a local Emmy award for his work in sports television in 2011.

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