The first full results from the Phase III Oxford COVID-19 vaccine have found it to be safe and effective to protect against the virus.
The Oxford COVID-19 vaccine has been found to protect against symptomatic cases of COVID-19 in 70% of cases, with the efficacy of 62% for those who received two full doses, and 90% in those given a half dose, and then a full dose.
During the trial, only three people out of the 23,745 participants over a median of 3.4 months experienced any adverse events that could have been related to the vaccine. All three participants have recovered or are recovering and remain in the trial.
Study lead author Professor Andrew Pollard, University of Oxford, UK, says: “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. Our findings indicate that our vaccine’s efficacy exceeds the thresholds set by health authorities and may have a potential public health impact.”
The results are the first full peer-reviewed efficacy results to be published for a COVID-19 vaccine and have been published in The Lancet.
Positive Phase III results
For this study, the authors analysed data from 23,745 adults in the UK, Brazil, and South Africa, with the analysis pooling data from these three countries which provides greater precision for efficacy and safety outcomes than possible in individual trials, and gives a broader understanding of the use of the vaccine in different populations. The majority of participants were aged 18 – 55 years, and people aged 56 years and older were recruited later. They will be studied in future analyses of the trial.
In the 11,636 people included in the vaccine efficacy against symptomatic disease analysis, 12% were older adults and 83% were white.
Study author, Dr Merryn Voysey, University of Oxford, UK, said: “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.”
How does the vaccine work?
The Oxford COVID-19 vaccine uses a chimpanzee adenovirus viral vector that expresses the SARS-CoV-2 spike protein but cannot cause disease in humans.
The vaccine delivers the spike protein genetic code into the cells of people being vaccinated and produces the protein, which teaches the immune system to recognise and attack the virus. Past trial results have found that the vaccine induces antibody and T-cell immune responses and is safe in adults aged 18 years and over, including older adults.
On all of the trial participants, cases of severe disease and hospitalisation were monitored for21 days after the first dose. There were 10 cases hospitalised for COVID-19, all in the control arm, and two were classified as severe, including one death. These are also secondary outcomes and will require additional confirmation.
Co-author, Professor Sarah Gilbert, University of Oxford, UK, commented: “Despite global spread of COVID-19, a large proportion of the population in many countries have not been infected and are not immune. Vaccines may play an important role in increasing immunity, preventing severe disease, and reducing the health crisis, so the possibility that more than one efficacious vaccine may be approved for use in the near future is encouraging. Here we have shown for the first time that an adenoviral vectored vaccine – a type of vaccine technology which has been in use since 2009 – is efficacious and could contribute to disease control in the COVID-19 pandemic.”
The authors have noted that they are not yet able to assess duration of protection, as the first trials were initiated in April 2020 and all disease episodes have accrued within six months of the first dose being administered.
