The high-level results from an interim analysis, including 131 Covid-19, have shown no hospitalisations or severe cases of the disease in participants receiving the vaccine.
AZD1222, co-invented by the University of Oxford and its spin-out company Vaccitech, uses a replication-deficient chimpanzee viral vector based on a weakened version of a common cold virus (adenovirus) that causes infections in chimpanzees and includes the genetic material of the SARS-CoV-2 virus spike protein.
One dosing regimen demonstrated vaccine efficacy of 90% when AZD1222 was delivered as a half dose, followed by a full dose at least one month apart.
Another dosing regimen showed 62% efficacy when delivered as two full doses at least one month apart. The combined analysis from both dosing regimens showed an average efficacy of 70%.
According to the company, an independent Data Safety Monitoring Board confirmed that the analysis achieved its primary endpoint demonstrating protection from Covid-19 occurring 14 days or more after securing two doses of the vaccine.
The company is also planning an emergency use listing (EUL) with the World Health Organisation (WHO) for an accelerated pathway to vaccine availability in low-income countries.
The pooled analysis comprised data from the COV002 phase II/III trial in the UK and COV003 phase III trial in Brazil.
More than 23,000 participants are being evaluated following two doses of either a half-dose/full-dose regimen or a regimen of two full doses of AZD1222 or a comparator, meningococcal conjugate vaccine called MenACWY or saline.
The global trials are assessing participants aged 18 years or over from diverse racial and geographic groups who are healthy or have stable underlying medical conditions.
In addition, clinical studies are being assessed in the US, Japan, Russia, South Africa, Kenya and Latin America with planned trials in other European and Asian countries.
AstraZeneca CEO Pascal Soriot said: “Today marks an important milestone in our fight against the pandemic. This vaccine’s efficacy and safety confirm that it will be highly effective against Covid-19 and will have an immediate impact on this public health emergency.
“Furthermore, the vaccine’s simple supply chain and our no-profit pledge and commitment to broad, equitable and timely access means it will be affordable and globally available, supplying hundreds of millions of doses on approval.”
Earlier this month, AstraZeneca announced that its Calquence (acalabrutinib) has failed to meet the primary efficacy endpoint in the CALAVI phase II trials, which evaluated patients hospitalised with respiratory symptoms of Covid-19.