The primary outcome was to determine how many cases of symptomatic COVID-19 disease there were in participants who had received two doses of the vaccine.
Interim results from the AstraZeneca/Oxford coronavirus disease 2019 (COVID-19) vaccine have been published in The Lancet, showing that the vaccine is safe and protects against the disease. The trial found that it protects against symptomatic disease in 70% of cases, with an efficacy of 62% for those given 2 doses and 90% for those given a half dose and then a full one.
There were 23,745 participants in the study from Brazil, South Africa and the UK, the majority aged between 18-55 years old. Half of them were given the vaccine and the other half were given a control. Only three of the participants out of the group experienced serious adverse side effects that may have been caused by the vaccine. They have all recovered or are currently recovering and are still in the trial.
“The results presented in this report provide the key findings from our first interim analysis,” Merryn Voysey, author on the study said. “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.”
The AstraZeneca/Oxford vaccine uses a chimpanzee adenovirus viral vector which cannot cause humans to contract the disease but expresses the SARS-CoV-2 spike protein. The vaccine delivers the genetic code into the cells, which in turn produce the protein and teaches the immune system to recognize and attack the virus.
The vaccine group in the study were each given two doses, containing 5x101 viral particles, while a subset in the UK only received a half dose for their first dose, followed by a full second dose. The study measured safety for 3.4 months, with participants experiencing 175 adverse events, but 172 of these were unrelated to the vaccine. Throughout the trial, there were 131 cases of symptomatic COVID-19 more than 14 days after the second dose, with 0.5% in the vaccine group and 1.7% in the control group. These equates to an efficacy rate of 70%.
“Control of the pandemic will only be achieved if the licensing, manufacturing and distribution of these vaccines can be achieved at an unprecedented scale and vaccination is rolled out to those who are vulnerable.” Andrew Pollard, lead author on the study said. “Our findings indicate that our vaccine’s efficacy exceeds the thresholds set by health authorities and may have a potential public health impact.”