AstraZeneca vaccine over 80% effective against severe disease, death after first dose, study shows

Real-world data from Canada shows 82 per cent and 87 per cent effectiveness after one dose of the vaccine against hospitalisation or death caused by the Beta/Gamma and Delta variants respectively.

The effectiveness of the AstraZeneca jab after one dose against hospitalisation or death was similar to that of other vaccines tested in the study. The follow-up time was not enough to report on its effectiveness after two doses, though other studies have shown increased effectiveness after two doses.

Vaxzevria was also found to be effective against milder symptomatic infection, though data was collected after the first dose. Vaccine effectiveness against any symptomatic disease was 50 per cent against Beta/Gamma variants and 70 per cent and 72 per cent against the Delta and Alpha variants respectively.

Trials carried out by the University of Oxford in the UK and the University of the Witwatersrand in South Africa in January showed limited efficacy against mild disease primarily due to the Beta variant. The study was unable to properly ascertain vaccine efficacy against severe disease, including hospitalisation and death, given that the subjects were predominantly young, healthy adults who only experienced mild symptoms.

Mene Pangalos, executive vice president of research and development at BioPharmaceuticals, said: “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. 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.”

The analysis included 69,533 individuals who tested positive for Covid-19 between December 2020 and May this year in Ontario, Canada. Of the subjects, 28,705 (6.8 per cent) tested positive for non-variants of concern and 40,828 (9.7 per cent) were positive for a variant of concern.

Vaxzevria, formerly AZD1222, was co-invented by the University of Oxford and its spin-out company, Vaccitech. It uses a replication-deficient chimpanzee viral vector based on a weakened version of a common cold virus (adenovirus) that causes infections in chimpanzees and contains the genetic material of the Covid-19 virus spike protein. After vaccination, the surface spike protein is produced, priming the immune system to attack the SARS-CoV-2 virus if it later infects the body.

The vaccine has been granted a conditional marketing authorisation or emergency use in more than 80 countries across six continents. More than 700 million doses of the vaccine have been supplied to 170 countries worldwide, including more than 100 countries through the Covax facility.