Results from the phase I/II blinded, multicenter, randomized clinical trial were published in The Lancet on July 20. The trial assessed immune responses of a single dose of AZD1222 in healthy adults aged 18 to 55 years. The study found a four-fold increase in antibodies against the SARS-CoV-2 spike protein in 95% of participants one month after vaccination.

Neutralizing antibody levels observed were similar to those seen in convalescent COVID-19 patients. The strongest immune responses were observed in participants who received low doses of the vaccine, suggesting that this might be the best vaccination strategy for the candidate. No serious adverse effects were reported with AZD1222.

Late-stage phase II/III trials for the vaccine candidate are currently underway in the U.K., Brazil, and South Africa, and are expected to begin soon in the U.S. These trials will aim to determine the appropriate dosage and further evaluate safety and immune responses.

Upon successful completion of clinical trials, AstraZeneca is committed to providing more than 2 billion doses of the vaccine as agreed upon by the U.K., U.S., Europe's Inclusive Vaccines Alliance, the Coalition for Epidemic Preparedness, Gavi the Vaccine Alliance, and Serum Institute of India.