New Delhi: 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.
The results, published Tuesday in The Lancet journal, are the first full peer-reviewed efficacy results to be published for a Covid-19 vaccine.
While Moderna has announced that its vaccine efficacy is over 94 per cent and the Pfizer vaccine has already got approval in the UK, neither has published the results of their trials in a peer-reviewed scientific journal.
The Oxford trials found that 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 that were possibly related to a vaccine, 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 Covid-19 vaccine uses a virus called ChAdOx1 — a weakened and non-replicating version of a common cold virus (adenovirus) — which infects chimpanzees but cannot cause disease in 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.
In India, the vaccine is being manufactured by the Serum Institute of India, which has also sought emergency use approval from the Government of India.
Also read: Approval, pricing, distribution — 5 questions India faces before rolling out Covid vaccine
The trial
For the study, the team analysed data from 23,745 adults in the UK, Brazil and South Africa. Half of the participants were given the Covid-19 vaccine and the other half were given a placebo.
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 future analysis of the trial.
The primary outcome of the study was to determine the cases of symptomatic Covid-19 disease that emerged in participants who had received two doses of the vaccine.
There were 131 cases of symptomatic Covid-19 disease more than 14 days after the second vaccine dose out of the 11,636 people. This included 30 cases in the vaccine group comprising 5,807 volunteers and 101 cases in the control group with 5,829 volunteers, which equates to a vaccine efficacy of 70 per cent.
The authors note that they have not been able to assess 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 duration of protection and the need for additional booster doses of the vaccine.
Also read: Pfizer Covid shot is highly effective, has no safety concerns, US FDA staff report says