AstraZeneca COVID-19 Vaccine Analysis Confirms Protection Against Severe Disease, Hospitalization, Death, Suggests Protection Against UK Variant


The clinical trials analyzed were from the United Kingdom, Brazil, and South Africa, where COVID-19 variants are of significant concern.

A primary analysis of phase 3 trials of the AstraZeneca coronavirus disease 2019 (COVID-19) vaccine has confirmed 100% protection against severe disease, hospitalization, and death, as well as more than 70% protection beginning after the first dose, according to a press release.1

Furthermore, in a paper released on Friday, researchers said the vaccine is effective against the variant known as B.1.1.7, found in the UK and recently identified in the United States.2 The clinical trials analyzed were from the United Kingdom, Brazil, and South Africa, where COVID-19 variants are of significant concern.1

According to the analysis of the vaccine, called ChAdOx1, there were no severe cases and no hospitalizations more than 22 days after the first dose, and the results demonstrated an efficacy of 76% after the first dose. The vaccine also has a longer inter-dose interval, with efficacy increasing to 82% after an inter-dose interval of 12 weeks or more.1

“This primary analysis reconfirms that our vaccine prevents severe disease and keeps people out of hospital,” said Mene Pangalos, BSc, PhD, executive vice president of biopharmaceuticals research and development at AstraZeneca, in a press release. “In addition, extending the dosing interval not only boosts the vaccine’s efficacy, but also enables more people to be vaccinated upfront. Together with the new findings on reduced transmission, we believe this vaccine will have a real impact on the pandemic.”1

Notably, the analysis also showed that the vaccine could potentially reduce asymptomatic transmission of COVID-19, based on weekly swabs from volunteers in the UK trial. According to a press release, positive polymerase chain reaction readings were reduced by 67% after a single dose and 50% after the 2-dose regimen, suggesting a substantial impact on transmission of the virus.1

This primary analysis was based on 17,177 participants who accrued 332 symptomatic cases from the phase 3 trials led by Oxford University and AstraZeneca. Data will continue to be analyzed and shared to support the ongoing rolling reviews for emergency supply or conditional approval, according to the press release. Importantly, the vaccine can be stored, transported, and handled at 36 to 46 degrees Fahrenheit for at least 6 months.1

“These new data provide an important verification of the interim data that has helped regulators such as the [Medicines and Healthcare Products Regulatory Agency] in the UK and elsewhere around the world to grant the vaccine emergency use authorization,” said Andrew Pollard, BSc, MBBS, PhD, chief investigator of the Oxford Vaccine Trial, in a press release. “It also helps to support the policy recommendation made by the Joint Committee on Vaccination and Immunization for a 12-week prime-boost interval, as they look for the optimal approach to roll out and reassures us that people are protected 22 days after a single dose of the vaccine.”1

In the paper released Friday, researchers said the vaccine has a 74.6% efficacy against the UK variant, a finding that is just slightly lower than its efficacy against other versions of the virus. The investigators sequenced the viral particles from 323 swabs between October 1, 2020, and January 14, 2021, during which time the variant was confirmed to be widespread in the UK.2

They found that while the vaccine had 84% efficacy against other lineages of the virus, it had 74.6% efficacy against the B.1.1.7 variant. Notably, however, the investigators said they did not have enough statistical evidence to know definitively whether the vaccine was slightly less effective against the variant.2

“Data from our trials of the ChAdOx1 vaccine in the United Kingdom indicate that the vaccine not only protects against the original pandemic virus, but also protects against the novel variant, B.1.1.7, which caused the surge in disease from the end of 2020 across the UK,” Pollard said, according to reporting by Reuters.3

The paper also showed that vaccination with the ChAdOx1 vaccine reduced the duration of shedding and viral load, which may lead to reduced transmission of the disease, according to the authors.2


  • COVID-19 Vaccine AstraZeneca confirms 100% protection against severe disease, hospitalization, and death in the primary analysis of Phase III trials [news release]. AstraZeneca; February 3, 202 Accessed February 5, 202
  • Emary K, Golubchik T, Aley P, et al. Efficacy of ChAdOx1 nCoV-19 (AZD1222) Vaccine Against SARS-CoV-2 VOC 202012-01 (B.1.1.7). The Lancet; February 4, 2021. Accessed February 5, 2021.
  • Oxford says COVID-19 vaccine with AstraZeneca works against UK variant. Reuters; February 5, 2021. Accessed February 5, 2021.

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