AstraZeneca’s investigational vaccine candidate AZD1222 was found to be safe and effective in preventing coronavirus disease 2019 (COVID-19), with no severe cases or hospitalizations reported more than 22 days after the first dose, according to primary analysis of three phase 3 trials.

AZD1222 utilizes a replication-deficient chimpanzee adenovirus to deliver a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) protein to induce a protective immune response. The 3 multicenter, randomized, controlled trials, COV002, COV003, and COV005, evaluated the efficacy, safety and immunogenicity of AZD1222 in over 24,000 participants aged 18 years and older in the United Kingdom (UK), Brazil, and South Africa, respectively. 

In the COV002 and COV003 trials, participants, who were healthy or had medically stable chronic diseases and were at increased risk of exposure to SARS-CoV-2 virus, were randomly assigned to receive 2 intramuscular (IM) doses of either a half-dose/full-dose regimen or a full-dose regimen of AZD1222 given at least 1 month apart or a comparator, meningococcal conjugate vaccine (MenACWY) or saline. In the COV005 trial, participants (with and without HIV) were randomly assigned to receive 2 IM doses of a full-dose regimen of AZD1222 given at least 1 month apart or saline.

Primary analysis of the trials (based on 17,177 participants and 332 symptomatic cases) showed that AZD1222 demonstrated vaccine efficacy of 76% (95% CI, 59-86) after the first dose, with protection maintained to the second dose. The vaccine efficacy increased to 82% (95% CI, 63-92) with an inter-dose interval of 12 weeks or more.

Additional analysis in the UK trial showed the potential of the vaccine to reduce asymptomatic transmission of the virus based on weekly swabs obtained from volunteers. After a single dose of the vaccine, results showed a 67% (95% CI, 49-78) reduction in PCR positive readings, and a 50% (95% CI, 38-59) reduction after the 2 dose regimen. Trial data will continue to be analyzed and shared with regulators. 

Sir Mene Pangalos, Executive Vice President BioPharmaceuticals R&D, said, “This primary analysis reconfirms that our vaccine prevents severe disease and keeps people out of hospital. In addition, extending the dosing interval not only boosts the vaccine’s efficacy, but also enables more people to be vaccinated upfront.”

The vaccine has already been granted a conditional marketing authorization or emergency use in close to 50 countries, including in the European Union, Latin American countries, India, Morocco, and the UK. The product can be stored, transported and handled at 2° to 8°C (36° to 46°F) for at least 6 months. 


COVID-19 vaccine AstraZeneca confirms 100% protection against severe disease, hospitalisation and death in the primary analysis of Phase III trials. [press release]. Cambridge, UK: AstraZeneca; February 3, 2021.