AstraZeneca’s Covid-19 Booster and Antibody Cocktail Retains Neutralizing Ability against Omicron

The Omicron variant has already become the dominant Covid-19 strain in the US, accounting for around 73% of recorded cases according to US Centers for Disease Control and Prevention (CDC) estimates. The variant’s large number of spike mutations has been shown to evade protection given by Covid-19 vaccines and antibody treatments which mainly target the spike protein. 

While boosters and a small handful of antibody therapies show some evidence of retaining activity against Omicron, their effect is still diminished compared to other strains such as Delta. 

AstraZeneca has recently reported that a third dose of its Covid-19 vaccine, Vaxzevria as well as its antibody cocktail Evusheld (tixagevimab/cilgavimab) retains neutralizing activity against Omicron. 

Vaxzevria Boosts Antibody Levels against Omicron 

A laboratory study conducted by the University of Oxford found that levels of neutralizing antibodies against Omicron were significantly increased after a third dose of Vaxzevria compared to the levels seen after a second dose. 

Serum samples taken from recipients of a third dose neutralized Omicron to levels that were similar to those observed one month after the second dose against the Delta variant. 

The study analyzed blood samples from people infected with Covid-19, been vaccinated with two doses and a booster, and those who had been previously infected with other variants.

The findings were published online on the bioRxiv preprint server. 

Evusheld Retains Neutralizing Activity

On December 16, an independent review by the FDA revealed that Evusheld, AstraZeneca’s approved antibody combination therapy, retained activity against the Omicron variant. The findings then were based on pseudovirus neutralization data, which tested Evusheld on genetically modified viruses designed to display the Omicron spike protein without the ability to self-replicate. 

Further research conducted by the University of Oxford and Washington University School of Medicine showed that Evusheld also displays neutralization activity against live viruses isolated from patients infected with Omicron. 

Evusheld’s Inhibitory Concentration 50 (IC50), a measure of neutralizing potency of an antibody, was 273 ng/ml and 147 ng/ml in the Oxford and Washington University studies respectively. The levels are within the range of neutralizing antibody titres found in individuals who have recovered from a previous Covid-19 infection. 

The US government has halted distribution of Regeneron’s REGEN-COV treatment and Eli Lilly’s bamlanivimab and etesevimab combo. Only a few antibody treatments show some evidence of retaining the ability to neutralize the Omicron variant. They include sotrovimab, developed by Vir Biotechnologies and GSK, DXP-604, an investigational treatment in China developed by BeiGene and Singlomics, and Brii Biosciences’ amubarvimab/romlusevimab, which has been approved by the NMPA for distribution in China. 

AstraZeneca is continuing its investigation of the efficacy of Vaxzevria and Evusheld against the Omicron variant. The company has said that it will submit data from both studies for peer review. 

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Joy Lin

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