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One dose of AZ’s COVID-19 vaccine ‘highly effective’ against severe disease from variants

New real-world data from Canada shows vaccine efficacy was lower against milder symptomatic disease with one dose

New real-world data has demonstrated that one dose of AstraZeneca’s COVID-19 vaccine is ‘highly effective’ at reducing severe disease and hospitalisation caused by variants of concern after one dose.

A pre-print study using real-world analysis – including 69,533 individuals who tested positive for COVID-19 through December 2020 to May 2021 in Ontario, Canada – showed one dose of AZ’s vaccine, named Vaxzevria in the EU, was 82% effective against hospitalisation or death caused by the Beta/Gamma variants.

According to the study, the vaccine showed an 87% reduction and 90% reduction of hospitalisation or death caused by the Delta and Alpha variants.

The follow-up time was not sufficient to provide insight into the effectiveness of the vaccine after two doses, although AZ said other studies have shown an increased effectiveness after the indicated two dose schedule.

Against milder symptomatic disease, AZ’s vaccine effectiveness was 50% against the Beta/Gamma variants and 70% and 72% against the Delta and Alpha variants, respectively.

Another study, from Public Health England (PHE), found earlier this week that two doses of the AZ vaccine or the Pfizer/BioNTech vaccine could protect against symptoms caused by the Alpha and Delta COVID-19 variants.

In the PHE study, two doses of the Pfizer/BioNTech vaccine were 93.7% effective at preventing symptomatic infections caused by the Alpha variant, and 88% against the Delta variant.

Meanwhile, two doses of the AZ vaccine were found to be 74.5% effective against symptomatic disease from the Alpha variant and 67% against the Delta variant.

Similar to the Canadian findings, the PHE researchers found that the effectiveness of either vaccine dropped if an individual had only received one dose – both jabs were found to be only around 48% effective against symptomatic disease caused by the Alpha variant and 30% against the Delta variant after one dose.

“Our finding of reduced effectiveness after the first dose would support efforts to maximise vaccine uptake with two doses among vulnerable groups in the context of circulation of the Delta variant,” commented the PHE researchers.

Article by
Lucy Parsons

23rd July 2021

From: Research



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