Only three out of 23,745 participants experienced serious adverse events
The interim results from the clinical trials of the Covid-19 vaccine, jointly developed by Oxford University and British-Swedish pharmaceutical company AstraZeneca, reveal that it protects against symptomatic disease in 70 per cent cases.
In India, the vaccine is being manufactured by the Serum Institute of India.
The results, published on Tuesday in The Lancet journal, are the first full peer-reviewed efficacy results to be published for a Covid-19 vaccine.
The trials found the vaccine efficacy is 62 per cent for those given two full doses, and 90 per cent in those given a half dose, followed by a full one.
Only three out of 23,745 participants, over an average of 3.4 months, experienced serious adverse events, the study reveals. Of these, one had received the vaccine arm while the other was in the placebo group.
“The results presented in this report provide the key findings from our first interim analysis. In future analyses, with more data included as it becomes available, we will investigate differences in key subgroups such as older adults, various ethnicities, doses, timing of booster vaccines, and we will determine which immune responses equate to protection from infection or disease,” Merryn Voysey, from the Oxford University and one of the study authors, said in a statement.
The Oxford vaccine uses ChAdOx1 — a weakened and non-replicating version of a common cold virus (adenovirus) — which infects chimpanzees, not humans.
The virus was engineered to express the SARS-CoV-2 spike protein, which means the vaccine delivers the spike protein genetic code into vaccinated people’s cells. The code then produces the protein and teaches the immune system to recognise and attack the virus.
The trial was originally designed to assess a single dose of the vaccine. However, a review of the immune response data in initial trials found that a second dose boosted immune responses. It was then modified and another dose was added to the trial protocol.
Most trial participants were aged 18-55 years. People aged 56 years and older were recruited later and will be studied in the future analysis of the trial.
The authors note that they have not been able to assess the duration of protection yet, as the first trials were initiated in April 2020 and all disease episodes occurred within six months of the first dose being administered.
Further evidence will be required to determine the duration of protection and the need for additional booster doses of the vaccine.