AstraZeneca COVID-19 Vaccine Effective Against Severe Disease With Certain Variants After Single Dose


One dose of AstraZeneca’s COVID-19 vaccine (Vaxzevria) was 82% effective against hospitalization or death caused by either the Beta or Gamma variants of the SARS-CoV-2 virus, according to data from the Canadian Immunization Research Network, currently published as a pre-print. According to the investigators, the vaccine also showed high levels of effectiveness against the Delta and Alpha variants, reducing risk of death and hospitalization by 87% and 90% respectively.

Although follow-up time was not sufficient to report on Vaxzevria’s effectiveness after 2 doses, other studies have demonstrated an increase in effectiveness when the 2 dose schedule is followed.

“With different variants threatening to disrupt our route out of the pandemic, this real-world evidence shows that Vaxzevria, along with other vaccines used in Canada, provides a high level of protection against the most serious forms of the disease, even after just one shot,” said Mene Pangalos, PhD, in a press release. “It is essential that we continue to protect as many people as possible in all corners of the world in order to get ahead of this deadly virus.”

Vaxzevria was also observed to be effective against milder symptomatic disease as well, though the data was only recorded after the first dose. Vaccine effectiveness against any symptomatic disease was 50% against the Beta and Gamma variants, and 70% and 72% against the Delta and Alpha variants, respectively.

The current study analyzed 69,533 individuals who tested positive for SARS-CoV-2 between December 2020 and May 2021 in Ontario, Canada. Of the patients studied, 28,705 tested positive for non-variants of concern, whereas 40,828 tested positive for variants of concern.

A previous phase 1/2 trial conducted in January had shown the vaccine had limited efficacy against mild disease, primarily due to the Beta variant. This study was also unable to ascertain vaccine efficacy against severe disease, including hospitalization and death, as the subjects were predominantly young, healthy adults who only experienced mild disease.


Vaxzevria is highly effective after one dose against severe disease or hospitalisation caused by Beta and Delta variants of concern [news release]. AstraZeneca; July 23, 2021. Accessed July 26, 2021.!

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